[syzbot] [cgroups?] possible deadlock in cgroup_free

[syzbot] [cgroups?] possible deadlock in cgroup_free

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f31817cbcf48 Add linux-next specific files for 20231116
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17d0aca7680000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
dashboard link: https://syzkaller.appspot.com/bug?extid=cef555184e66963dabc2
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/987488cb251e/disk-f31817cb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6d4a82d8bd4b/vmlinux-f31817cb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc43dee9cb86/bzImage-f31817cb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cef555184e66963dabc2@syzkaller.appspotmail.com

=====================================================
WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
6.7.0-rc1-next-20231116-syzkaller #0 Not tainted
-----------------------------------------------------
syz-executor.3/8188 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
ffff88801f641298 (&sighand->siglock){+.+.}-{2:2}, at: __lock_task_sighand+0xc2/0x340 kernel/signal.c:1422

and this task is already holding:
ffffffff8cff86b8 (css_set_lock){..-.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:376 [inline]
ffffffff8cff86b8 (css_set_lock){..-.}-{2:2}, at: cgroup_migrate_execute+0xd8/0x1230 kernel/cgroup/cgroup.c:2566
which would create a new lock dependency:
 (css_set_lock){..-.}-{2:2} -> (&sighand->siglock){+.+.}-{2:2}

but this new dependency connects a SOFTIRQ-irq-safe lock:
 (css_set_lock){..-.}-{2:2}

... which became SOFTIRQ-irq-safe at:
  lock_acquire kernel/locking/lockdep.c:5753 [inline]
  lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
  _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
  put_css_set kernel/cgroup/cgroup-internal.h:208 [inline]
  put_css_set kernel/cgroup/cgroup-internal.h:196 [inline]
  cgroup_free+0x7c/0x1d0 kernel/cgroup/cgroup.c:6748
  __put_task_struct+0x10b/0x3d0 kernel/fork.c:992
  put_task_struct include/linux/sched/task.h:136 [inline]
  put_task_struct include/linux/sched/task.h:123 [inline]
  delayed_put_task_struct+0x22c/0x2d0 kernel/exit.c:227
  rcu_do_batch kernel/rcu/tree.c:2158 [inline]
  rcu_core+0x828/0x16b0 kernel/rcu/tree.c:2431
  __do_softirq+0x216/0x8d5 kernel/softirq.c:553
  invoke_softirq kernel/softirq.c:427 [inline]
  __irq_exit_rcu kernel/softirq.c:632 [inline]
  irq_exit_rcu+0xb5/0x120 kernel/softirq.c:644
  sysvec_apic_timer_interrupt+0x95/0xb0 arch/x86/kernel/apic/apic.c:1076
  asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
  lock_acquire+0x1f2/0x530 kernel/locking/lockdep.c:5721
  __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
  _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
  spin_lock include/linux/spinlock.h:351 [inline]
  lockref_put_or_lock+0x18/0x80 lib/lockref.c:147
  fast_dput fs/dcache.c:775 [inline]
  fast_dput fs/dcache.c:765 [inline]
  dput+0x4c4/0xd90 fs/dcache.c:900
  shmem_unlink+0x1bc/0x310 mm/shmem.c:3373
  shmem_rename2+0x1ff/0x3b0 mm/shmem.c:3451
  vfs_rename+0xe20/0x1c30 fs/namei.c:4844
  do_renameat2+0xc3c/0xdc0 fs/namei.c:4996
  __do_sys_rename fs/namei.c:5042 [inline]
  __se_sys_rename fs/namei.c:5040 [inline]
  __x64_sys_rename+0x81/0xa0 fs/namei.c:5040
  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
  do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
  entry_SYSCALL_64_after_hwframe+0x62/0x6a

to a SOFTIRQ-irq-unsafe lock:
 (&sighand->siglock){+.+.}-{2:2}

... which became SOFTIRQ-irq-unsafe at:
...
  lock_acquire kernel/locking/lockdep.c:5753 [inline]
  lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
  __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
  _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
  spin_lock include/linux/spinlock.h:351 [inline]
  class_spinlock_constructor include/linux/spinlock.h:530 [inline]
  ptrace_set_stopped kernel/ptrace.c:391 [inline]
  ptrace_attach+0x401/0x650 kernel/ptrace.c:478
  __do_sys_ptrace+0x204/0x230 kernel/ptrace.c:1290
  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
  do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
  entry_SYSCALL_64_after_hwframe+0x62/0x6a

other info that might help us debug this:

 Possible interrupt unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sighand->siglock);
                               local_irq_disable();
                               lock(css_set_lock);
                               lock(&sighand->siglock);
  <Interrupt>
    lock(css_set_lock);

 *** DEADLOCK ***

8 locks held by syz-executor.3/8188:
 #0: ffff88801d0e0d48 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe7/0x170 fs/file.c:1177
 #1: ffff888014b44420 (sb_writers#10){.+.+}-{0:0}, at: ksys_write+0x12f/0x250 fs/read_write.c:637
 #2: ffff88807ad7f088 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x27d/0x500 fs/kernfs/file.c:325
 #3: ffffffff8cff8768 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_lock include/linux/cgroup.h:368 [inline]
 #3: ffffffff8cff8768 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_lock_and_drain_offline+0xad/0x6d0 kernel/cgroup/cgroup.c:3092
 #4: ffffffff8ce51f70 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2413 [inline]
 #4: ffffffff8ce51f70 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_update_dfl_csses+0x2fb/0x640 kernel/cgroup/cgroup.c:3050
 #5: ffffffff8cff8530 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2415 [inline]
 #5: ffffffff8cff8530 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2411 [inline]
 #5: ffffffff8cff8530 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: cgroup_update_dfl_csses+0x3d1/0x640 kernel/cgroup/cgroup.c:3050
 #6: ffffffff8cff86b8 (css_set_lock){..-.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:376 [inline]
 #6: ffffffff8cff86b8 (css_set_lock){..-.}-{2:2}, at: cgroup_migrate_execute+0xd8/0x1230 kernel/cgroup/cgroup.c:2566
 #7: ffffffff8cfad060 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:301 [inline]
 #7: ffffffff8cfad060 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]
 #7: ffffffff8cfad060 (rcu_read_lock){....}-{1:2}, at: __lock_task_sighand+0x3f/0x340 kernel/signal.c:1405

the dependencies between SOFTIRQ-irq-safe lock and the holding lock:
-> (css_set_lock){..-.}-{2:2} {
   IN-SOFTIRQ-W at:
                    lock_acquire kernel/locking/lockdep.c:5753 [inline]
                    lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                    __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
                    _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
                    put_css_set kernel/cgroup/cgroup-internal.h:208 [inline]
                    put_css_set kernel/cgroup/cgroup-internal.h:196 [inline]
                    cgroup_free+0x7c/0x1d0 kernel/cgroup/cgroup.c:6748
                    __put_task_struct+0x10b/0x3d0 kernel/fork.c:992
                    put_task_struct include/linux/sched/task.h:136 [inline]
                    put_task_struct include/linux/sched/task.h:123 [inline]
                    delayed_put_task_struct+0x22c/0x2d0 kernel/exit.c:227
                    rcu_do_batch kernel/rcu/tree.c:2158 [inline]
                    rcu_core+0x828/0x16b0 kernel/rcu/tree.c:2431
                    __do_softirq+0x216/0x8d5 kernel/softirq.c:553
                    invoke_softirq kernel/softirq.c:427 [inline]
                    __irq_exit_rcu kernel/softirq.c:632 [inline]
                    irq_exit_rcu+0xb5/0x120 kernel/softirq.c:644
                    sysvec_apic_timer_interrupt+0x95/0xb0 arch/x86/kernel/apic/apic.c:1076
                    asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
                    lock_acquire+0x1f2/0x530 kernel/locking/lockdep.c:5721
                    __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
                    _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
                    spin_lock include/linux/spinlock.h:351 [inline]
                    lockref_put_or_lock+0x18/0x80 lib/lockref.c:147
                    fast_dput fs/dcache.c:775 [inline]
                    fast_dput fs/dcache.c:765 [inline]
                    dput+0x4c4/0xd90 fs/dcache.c:900
                    shmem_unlink+0x1bc/0x310 mm/shmem.c:3373
                    shmem_rename2+0x1ff/0x3b0 mm/shmem.c:3451
                    vfs_rename+0xe20/0x1c30 fs/namei.c:4844
                    do_renameat2+0xc3c/0xdc0 fs/namei.c:4996
                    __do_sys_rename fs/namei.c:5042 [inline]
                    __se_sys_rename fs/namei.c:5040 [inline]
                    __x64_sys_rename+0x81/0xa0 fs/namei.c:5040
                    do_syscall_x64 arch/x86/entry/common.c:51 [inline]
                    do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
                    entry_SYSCALL_64_after_hwframe+0x62/0x6a
   INITIAL USE at:
                   lock_acquire kernel/locking/lockdep.c:5753 [inline]
                   lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                   __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
                   _raw_spin_lock_irq+0x36/0x50 kernel/locking/spinlock.c:170
                   spin_lock_irq include/linux/spinlock.h:376 [inline]
                   cgroup_setup_root+0x62c/0xa00 kernel/cgroup/cgroup.c:2138
                   cgroup_init+0x23f/0x1100 kernel/cgroup/cgroup.c:6120
                   start_kernel+0x385/0x480 init/main.c:1063
                   x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:555
                   x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:536
                   secondary_startup_64_no_verify+0x166/0x16b
 }
 ... key      at: [<ffffffff8cff86b8>] css_set_lock+0x18/0x60

the dependencies between the lock to be acquired
 and SOFTIRQ-irq-unsafe lock:
-> (&sighand->siglock){+.+.}-{2:2} {
   HARDIRQ-ON-W at:
                    lock_acquire kernel/locking/lockdep.c:5753 [inline]
                    lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                    __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
                    _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
                    spin_lock include/linux/spinlock.h:351 [inline]
                    class_spinlock_constructor include/linux/spinlock.h:530 [inline]
                    ptrace_set_stopped kernel/ptrace.c:391 [inline]
                    ptrace_attach+0x401/0x650 kernel/ptrace.c:478
                    __do_sys_ptrace+0x204/0x230 kernel/ptrace.c:1290
                    do_syscall_x64 arch/x86/entry/common.c:51 [inline]
                    do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
                    entry_SYSCALL_64_after_hwframe+0x62/0x6a
   SOFTIRQ-ON-W at:
                    lock_acquire kernel/locking/lockdep.c:5753 [inline]
                    lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                    __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
                    _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
                    spin_lock include/linux/spinlock.h:351 [inline]
                    class_spinlock_constructor include/linux/spinlock.h:530 [inline]
                    ptrace_set_stopped kernel/ptrace.c:391 [inline]
                    ptrace_attach+0x401/0x650 kernel/ptrace.c:478
                    __do_sys_ptrace+0x204/0x230 kernel/ptrace.c:1290
                    do_syscall_x64 arch/x86/entry/common.c:51 [inline]
                    do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
                    entry_SYSCALL_64_after_hwframe+0x62/0x6a
   INITIAL USE at:
                   lock_acquire kernel/locking/lockdep.c:5753 [inline]
                   lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                   __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
                   _raw_spin_lock_irq+0x36/0x50 kernel/locking/spinlock.c:170
                   spin_lock_irq include/linux/spinlock.h:376 [inline]
                   calculate_sigpending+0x44/0xa0 kernel/signal.c:197
                   ret_from_fork+0x23/0x80 arch/x86/kernel/process.c:143
                   ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
 }
 ... key      at: [<ffffffff90b49f80>] __key.341+0x0/0x40
 ... acquired at:
   lock_acquire kernel/locking/lockdep.c:5753 [inline]
   lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
   __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
   _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
   __lock_task_sighand+0xc2/0x340 kernel/signal.c:1422
   lock_task_sighand include/linux/sched/signal.h:748 [inline]
   cgroup_freeze_task+0x80/0x190 kernel/cgroup/freezer.c:160
   cgroup_freezer_migrate_task+0x1b7/0x3a0 kernel/cgroup/freezer.c:257
   cgroup_migrate_execute+0x2d3/0x1230 kernel/cgroup/cgroup.c:2580
   cgroup_update_dfl_csses+0x51b/0x640 kernel/cgroup/cgroup.c:3068
   cgroup_apply_control kernel/cgroup/cgroup.c:3308 [inline]
   cgroup_subtree_control_write+0xb94/0xed0 kernel/cgroup/cgroup.c:3453
   cgroup_file_write+0x209/0x7c0 kernel/cgroup/cgroup.c:4092
   kernfs_fop_write_iter+0x33f/0x500 fs/kernfs/file.c:334
   call_write_iter include/linux/fs.h:2021 [inline]
   new_sync_write fs/read_write.c:491 [inline]
   vfs_write+0x64d/0xdf0 fs/read_write.c:584
   ksys_write+0x12f/0x250 fs/read_write.c:637
   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
   do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
   entry_SYSCALL_64_after_hwframe+0x62/0x6a


stack backtrace:
CPU: 1 PID: 8188 Comm: syz-executor.3 Not tainted 6.7.0-rc1-next-20231116-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
 print_bad_irq_dependency kernel/locking/lockdep.c:2626 [inline]
 check_irq_usage+0xe18/0x1470 kernel/locking/lockdep.c:2865
 check_prev_add kernel/locking/lockdep.c:3138 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain kernel/locking/lockdep.c:3868 [inline]
 __lock_acquire+0x247c/0x3b10 kernel/locking/lockdep.c:5136
 lock_acquire kernel/locking/lockdep.c:5753 [inline]
 lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
 __lock_task_sighand+0xc2/0x340 kernel/signal.c:1422
 lock_task_sighand include/linux/sched/signal.h:748 [inline]
 cgroup_freeze_task+0x80/0x190 kernel/cgroup/freezer.c:160
 cgroup_freezer_migrate_task+0x1b7/0x3a0 kernel/cgroup/freezer.c:257
 cgroup_migrate_execute+0x2d3/0x1230 kernel/cgroup/cgroup.c:2580
 cgroup_update_dfl_csses+0x51b/0x640 kernel/cgroup/cgroup.c:3068
 cgroup_apply_control kernel/cgroup/cgroup.c:3308 [inline]
 cgroup_subtree_control_write+0xb94/0xed0 kernel/cgroup/cgroup.c:3453
 cgroup_file_write+0x209/0x7c0 kernel/cgroup/cgroup.c:4092
 kernfs_fop_write_iter+0x33f/0x500 fs/kernfs/file.c:334
 call_write_iter include/linux/fs.h:2021 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x64d/0xdf0 fs/read_write.c:584
 ksys_write+0x12f/0x250 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x62/0x6a
RIP: 0033:0x7f83f387cae9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f83f466d0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f83f399bf80 RCX: 00007f83f387cae9
RDX: 0000000000000006 RSI: 0000000020000100 RDI: 0000000000000004
RBP: 00007f83f38c847a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f83f399bf80 R15: 00007ffdda059fd8
 </TASK>


---
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Re: [syzbot] [cgroups?] possible deadlock in cgroup_free

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    f31817cbcf48 Add linux-next specific files for 20231116
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=14fa5a48e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
dashboard link: https://syzkaller.appspot.com/bug?extid=cef555184e66963dabc2
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13fd7920e80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17d80920e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/987488cb251e/disk-f31817cb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6d4a82d8bd4b/vmlinux-f31817cb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc43dee9cb86/bzImage-f31817cb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cef555184e66963dabc2@syzkaller.appspotmail.com

========================================================
WARNING: possible irq lock inversion dependency detected
6.7.0-rc1-next-20231116-syzkaller #0 Not tainted
--------------------------------------------------------
swapper/0/0 just changed the state of lock:
ffffffff8cff86b8 (css_set_lock){..-.}-{2:2}, at: put_css_set kernel/cgroup/cgroup-internal.h:208 [inline]
ffffffff8cff86b8 (css_set_lock){..-.}-{2:2}, at: put_css_set kernel/cgroup/cgroup-internal.h:196 [inline]
ffffffff8cff86b8 (css_set_lock){..-.}-{2:2}, at: cgroup_free+0x7c/0x1d0 kernel/cgroup/cgroup.c:6748
but this lock took another, SOFTIRQ-unsafe lock in the past:
 (&sighand->siglock){+.+.}-{2:2}


and interrupts could create inverse lock ordering between them.


other info that might help us debug this:
 Possible interrupt unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sighand->siglock);
                               local_irq_disable();
                               lock(css_set_lock);
                               lock(&sighand->siglock);
  <Interrupt>
    lock(css_set_lock);

 *** DEADLOCK ***

2 locks held by swapper/0/0:
 #0: ffffffff8cfacf40 (rcu_callback){....}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:301 [inline]
 #0: ffffffff8cfacf40 (rcu_callback){....}-{0:0}, at: rcu_do_batch kernel/rcu/tree.c:2152 [inline]
 #0: ffffffff8cfacf40 (rcu_callback){....}-{0:0}, at: rcu_core+0x7cc/0x16b0 kernel/rcu/tree.c:2431
 #1: ffffffff8ce58800 (put_task_map-wait-type-override){+...}-{3:3}, at: put_task_struct include/linux/sched/task.h:135 [inline]
 #1: ffffffff8ce58800 (put_task_map-wait-type-override){+...}-{3:3}, at: put_task_struct include/linux/sched/task.h:123 [inline]
 #1: ffffffff8ce58800 (put_task_map-wait-type-override){+...}-{3:3}, at: delayed_put_task_struct+0x21e/0x2d0 kernel/exit.c:227

the shortest dependencies between 2nd lock and 1st lock:
 -> (&sighand->siglock){+.+.}-{2:2} {
    HARDIRQ-ON-W at:
                      lock_acquire kernel/locking/lockdep.c:5753 [inline]
                      lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                      __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
                      _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
                      spin_lock include/linux/spinlock.h:351 [inline]
                      class_spinlock_constructor include/linux/spinlock.h:530 [inline]
                      ptrace_set_stopped kernel/ptrace.c:391 [inline]
                      ptrace_attach+0x401/0x650 kernel/ptrace.c:478
                      __do_sys_ptrace+0x204/0x230 kernel/ptrace.c:1290
                      do_syscall_x64 arch/x86/entry/common.c:51 [inline]
                      do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
                      entry_SYSCALL_64_after_hwframe+0x62/0x6a
    SOFTIRQ-ON-W at:
                      lock_acquire kernel/locking/lockdep.c:5753 [inline]
                      lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                      __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
                      _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
                      spin_lock include/linux/spinlock.h:351 [inline]
                      class_spinlock_constructor include/linux/spinlock.h:530 [inline]
                      ptrace_set_stopped kernel/ptrace.c:391 [inline]
                      ptrace_attach+0x401/0x650 kernel/ptrace.c:478
                      __do_sys_ptrace+0x204/0x230 kernel/ptrace.c:1290
                      do_syscall_x64 arch/x86/entry/common.c:51 [inline]
                      do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
                      entry_SYSCALL_64_after_hwframe+0x62/0x6a
    INITIAL USE at:
                     lock_acquire kernel/locking/lockdep.c:5753 [inline]
                     lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                     __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
                     _raw_spin_lock_irq+0x36/0x50 kernel/locking/spinlock.c:170
                     spin_lock_irq include/linux/spinlock.h:376 [inline]
                     calculate_sigpending+0x44/0xa0 kernel/signal.c:197
                     ret_from_fork+0x23/0x80 arch/x86/kernel/process.c:143
                     ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
  }
  ... key      at: [<ffffffff90b49f80>] __key.341+0x0/0x40
  ... acquired at:
   __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
   _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
   __lock_task_sighand+0xc2/0x340 kernel/signal.c:1422
   lock_task_sighand include/linux/sched/signal.h:748 [inline]
   cgroup_freeze_task+0x80/0x190 kernel/cgroup/freezer.c:160
   cgroup_freezer_migrate_task+0x1b7/0x3a0 kernel/cgroup/freezer.c:257
   cgroup_migrate_execute+0x2d3/0x1230 kernel/cgroup/cgroup.c:2580
   cgroup_update_dfl_csses+0x51b/0x640 kernel/cgroup/cgroup.c:3068
   cgroup_apply_control kernel/cgroup/cgroup.c:3308 [inline]
   cgroup_subtree_control_write+0xb94/0xed0 kernel/cgroup/cgroup.c:3453
   cgroup_file_write+0x209/0x7c0 kernel/cgroup/cgroup.c:4092
   kernfs_fop_write_iter+0x33f/0x500 fs/kernfs/file.c:334
   call_write_iter include/linux/fs.h:2021 [inline]
   new_sync_write fs/read_write.c:491 [inline]
   vfs_write+0x64d/0xdf0 fs/read_write.c:584
   ksys_write+0x12f/0x250 fs/read_write.c:637
   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
   do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
   entry_SYSCALL_64_after_hwframe+0x62/0x6a

-> (css_set_lock){..-.}-{2:2} {
   IN-SOFTIRQ-W at:
                    lock_acquire kernel/locking/lockdep.c:5753 [inline]
                    lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                    __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
                    _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
                    put_css_set kernel/cgroup/cgroup-internal.h:208 [inline]
                    put_css_set kernel/cgroup/cgroup-internal.h:196 [inline]
                    cgroup_free+0x7c/0x1d0 kernel/cgroup/cgroup.c:6748
                    __put_task_struct+0x10b/0x3d0 kernel/fork.c:992
                    put_task_struct include/linux/sched/task.h:136 [inline]
                    put_task_struct include/linux/sched/task.h:123 [inline]
                    delayed_put_task_struct+0x22c/0x2d0 kernel/exit.c:227
                    rcu_do_batch kernel/rcu/tree.c:2158 [inline]
                    rcu_core+0x828/0x16b0 kernel/rcu/tree.c:2431
                    __do_softirq+0x216/0x8d5 kernel/softirq.c:553
                    invoke_softirq kernel/softirq.c:427 [inline]
                    __irq_exit_rcu kernel/softirq.c:632 [inline]
                    irq_exit_rcu+0xb5/0x120 kernel/softirq.c:644
                    sysvec_apic_timer_interrupt+0x95/0xb0 arch/x86/kernel/apic/apic.c:1076
                    asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
                    native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
                    arch_safe_halt arch/x86/include/asm/irqflags.h:86 [inline]
                    acpi_safe_halt+0x1a/0x20 drivers/acpi/processor_idle.c:112
                    acpi_idle_enter+0xc5/0x160 drivers/acpi/processor_idle.c:707
                    cpuidle_enter_state+0x83/0x500 drivers/cpuidle/cpuidle.c:267
                    cpuidle_enter+0x4e/0xa0 drivers/cpuidle/cpuidle.c:388
                    cpuidle_idle_call kernel/sched/idle.c:215 [inline]
                    do_idle+0x314/0x3f0 kernel/sched/idle.c:312
                    cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:410
                    rest_init+0x16f/0x2b0 init/main.c:730
                    arch_call_rest_init+0x13/0x30 init/main.c:827
                    start_kernel+0x39e/0x480 init/main.c:1072
                    x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:555
                    x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:536
                    secondary_startup_64_no_verify+0x166/0x16b
   INITIAL USE at:
                   lock_acquire kernel/locking/lockdep.c:5753 [inline]
                   lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
                   __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
                   _raw_spin_lock_irq+0x36/0x50 kernel/locking/spinlock.c:170
                   spin_lock_irq include/linux/spinlock.h:376 [inline]
                   cgroup_setup_root+0x62c/0xa00 kernel/cgroup/cgroup.c:2138
                   cgroup_init+0x23f/0x1100 kernel/cgroup/cgroup.c:6120
                   start_kernel+0x385/0x480 init/main.c:1063
                   x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:555
                   x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:536
                   secondary_startup_64_no_verify+0x166/0x16b
 }
 ... key      at: [<ffffffff8cff86b8>] css_set_lock+0x18/0x60
 ... acquired at:
   mark_usage kernel/locking/lockdep.c:4566 [inline]
   __lock_acquire+0x13c2/0x3b10 kernel/locking/lockdep.c:5090
   lock_acquire kernel/locking/lockdep.c:5753 [inline]
   lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
   __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
   _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
   put_css_set kernel/cgroup/cgroup-internal.h:208 [inline]
   put_css_set kernel/cgroup/cgroup-internal.h:196 [inline]
   cgroup_free+0x7c/0x1d0 kernel/cgroup/cgroup.c:6748
   __put_task_struct+0x10b/0x3d0 kernel/fork.c:992
   put_task_struct include/linux/sched/task.h:136 [inline]
   put_task_struct include/linux/sched/task.h:123 [inline]
   delayed_put_task_struct+0x22c/0x2d0 kernel/exit.c:227
   rcu_do_batch kernel/rcu/tree.c:2158 [inline]
   rcu_core+0x828/0x16b0 kernel/rcu/tree.c:2431
   __do_softirq+0x216/0x8d5 kernel/softirq.c:553
   invoke_softirq kernel/softirq.c:427 [inline]
   __irq_exit_rcu kernel/softirq.c:632 [inline]
   irq_exit_rcu+0xb5/0x120 kernel/softirq.c:644
   sysvec_apic_timer_interrupt+0x95/0xb0 arch/x86/kernel/apic/apic.c:1076
   asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
   native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
   arch_safe_halt arch/x86/include/asm/irqflags.h:86 [inline]
   acpi_safe_halt+0x1a/0x20 drivers/acpi/processor_idle.c:112
   acpi_idle_enter+0xc5/0x160 drivers/acpi/processor_idle.c:707
   cpuidle_enter_state+0x83/0x500 drivers/cpuidle/cpuidle.c:267
   cpuidle_enter+0x4e/0xa0 drivers/cpuidle/cpuidle.c:388
   cpuidle_idle_call kernel/sched/idle.c:215 [inline]
   do_idle+0x314/0x3f0 kernel/sched/idle.c:312
   cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:410
   rest_init+0x16f/0x2b0 init/main.c:730
   arch_call_rest_init+0x13/0x30 init/main.c:827
   start_kernel+0x39e/0x480 init/main.c:1072
   x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:555
   x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:536
   secondary_startup_64_no_verify+0x166/0x16b


stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.7.0-rc1-next-20231116-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
 print_irq_inversion_bug.part.0+0x3e1/0x590 kernel/locking/lockdep.c:4079
 print_irq_inversion_bug kernel/locking/lockdep.c:4032 [inline]
 check_usage_forwards kernel/locking/lockdep.c:4110 [inline]
 mark_lock_irq kernel/locking/lockdep.c:4242 [inline]
 mark_lock+0x570/0xc50 kernel/locking/lockdep.c:4677
 mark_usage kernel/locking/lockdep.c:4566 [inline]
 __lock_acquire+0x13c2/0x3b10 kernel/locking/lockdep.c:5090
 lock_acquire kernel/locking/lockdep.c:5753 [inline]
 lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
 put_css_set kernel/cgroup/cgroup-internal.h:208 [inline]
 put_css_set kernel/cgroup/cgroup-internal.h:196 [inline]
 cgroup_free+0x7c/0x1d0 kernel/cgroup/cgroup.c:6748
 __put_task_struct+0x10b/0x3d0 kernel/fork.c:992
 put_task_struct include/linux/sched/task.h:136 [inline]
 put_task_struct include/linux/sched/task.h:123 [inline]
 delayed_put_task_struct+0x22c/0x2d0 kernel/exit.c:227
 rcu_do_batch kernel/rcu/tree.c:2158 [inline]
 rcu_core+0x828/0x16b0 kernel/rcu/tree.c:2431
 __do_softirq+0x216/0x8d5 kernel/softirq.c:553
 invoke_softirq kernel/softirq.c:427 [inline]
 __irq_exit_rcu kernel/softirq.c:632 [inline]
 irq_exit_rcu+0xb5/0x120 kernel/softirq.c:644
 sysvec_apic_timer_interrupt+0x95/0xb0 arch/x86/kernel/apic/apic.c:1076
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
RIP: 0010:native_irq_disable arch/x86/include/asm/irqflags.h:37 [inline]
RIP: 0010:arch_local_irq_disable arch/x86/include/asm/irqflags.h:72 [inline]
RIP: 0010:acpi_safe_halt+0x1a/0x20 drivers/acpi/processor_idle.c:113
Code: 08 ed c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 65 48 8b 05 a8 8a 82 75 48 8b 00 a8 08 75 0c 66 90 0f 00 2d 78 0a b9 00 fb f4 <fa> c3 0f 1f 40 00 0f b6 47 08 3c 01 74 0b 3c 02 74 05 8b 7f 04 eb
RSP: 0018:ffffffff8cc07d68 EFLAGS: 00000246
RAX: 0000000000004000 RBX: 0000000000000001 RCX: ffffffff8a8117f5
RDX: 0000000000000001 RSI: ffff8880156c2800 RDI: ffff8880156c2864
RBP: ffff8880156c2864 R08: 0000000000000001 R09: ffffed1017306dbd
R10: ffff8880b9836deb R11: 0000000000000000 R12: ffff888147ac4000
R13: ffffffff8db1a520 R14: 0000000000000000 R15: 0000000000000000
 acpi_idle_enter+0xc5/0x160 drivers/acpi/processor_idle.c:707
 cpuidle_enter_state+0x83/0x500 drivers/cpuidle/cpuidle.c:267
 cpuidle_enter+0x4e/0xa0 drivers/cpuidle/cpuidle.c:388
 cpuidle_idle_call kernel/sched/idle.c:215 [inline]
 do_idle+0x314/0x3f0 kernel/sched/idle.c:312
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:410
 rest_init+0x16f/0x2b0 init/main.c:730
 arch_call_rest_init+0x13/0x30 init/main.c:827
 start_kernel+0x39e/0x480 init/main.c:1072
 x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:555
 x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:536
 secondary_startup_64_no_verify+0x166/0x16b
 </TASK>
----------------
Code disassembly (best guess):
   0:	08 ed                	or     %ch,%ch
   2:	c3                   	ret
   3:	66 66 2e 0f 1f 84 00 	data16 cs nopw 0x0(%rax,%rax,1)
   a:	00 00 00 00
   e:	66 90                	xchg   %ax,%ax
  10:	65 48 8b 05 a8 8a 82 	mov    %gs:0x75828aa8(%rip),%rax        # 0x75828ac0
  17:	75
  18:	48 8b 00             	mov    (%rax),%rax
  1b:	a8 08                	test   $0x8,%al
  1d:	75 0c                	jne    0x2b
  1f:	66 90                	xchg   %ax,%ax
  21:	0f 00 2d 78 0a b9 00 	verw   0xb90a78(%rip)        # 0xb90aa0
  28:	fb                   	sti
  29:	f4                   	hlt
* 2a:	fa                   	cli <-- trapping instruction
  2b:	c3                   	ret
  2c:	0f 1f 40 00          	nopl   0x0(%rax)
  30:	0f b6 47 08          	movzbl 0x8(%rdi),%eax
  34:	3c 01                	cmp    $0x1,%al
  36:	74 0b                	je     0x43
  38:	3c 02                	cmp    $0x2,%al
  3a:	74 05                	je     0x41
  3c:	8b 7f 04             	mov    0x4(%rdi),%edi
  3f:	eb                   	.byte 0xeb


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [cgroups?] possible deadlock in cgroup_free

[syzbot]

syzbot has bisected this issue to:

commit 2d25a889601d2fbc87ec79b30ea315820f874b78
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Sun Sep 17 11:24:21 2023 +0000

    ptrace: Convert ptrace_attach() to use lock guards

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=130edb3f680000
start commit:   f31817cbcf48 Add linux-next specific files for 20231116
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=108edb3f680000
console output: https://syzkaller.appspot.com/x/log.txt?x=170edb3f680000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
dashboard link: https://syzkaller.appspot.com/bug?extid=cef555184e66963dabc2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13fd7920e80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17d80920e80000

Reported-by: syzbot+cef555184e66963dabc2@syzkaller.appspotmail.com
Fixes: 2d25a889601d ("ptrace: Convert ptrace_attach() to use lock guards")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] Test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Test
Author: tintinm2017@gmail.com

#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Re: [syzbot] [cgroups?] possible deadlock in cgroup_free

[Tejun Heo]

On Thu, Nov 16, 2023 at 05:25:05PM -0800, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit 2d25a889601d2fbc87ec79b30ea315820f874b78
> Author: Peter Zijlstra <peterz@infradead.org>
> Date:   Sun Sep 17 11:24:21 2023 +0000
> 
>     ptrace: Convert ptrace_attach() to use lock guards

Looks like the tasklist_lock conversion in ptrace_attach() forgot _irq.
Peter, Oleg?

Thanks.

-- 
tejun

Re: [syzbot] [cgroups?] possible deadlock in cgroup_free

[Oleg Nesterov]

On 11/19, Tejun Heo wrote:
>
> On Thu, Nov 16, 2023 at 05:25:05PM -0800, syzbot wrote:
> > syzbot has bisected this issue to:
> >
> > commit 2d25a889601d2fbc87ec79b30ea315820f874b78
> > Author: Peter Zijlstra <peterz@infradead.org>
> > Date:   Sun Sep 17 11:24:21 2023 +0000
> >
> >     ptrace: Convert ptrace_attach() to use lock guards
>
> Looks like the tasklist_lock conversion in ptrace_attach() forgot _irq.
> Peter, Oleg?

Yes, please see

	Re: [syzbot] [kernel?] inconsistent lock state in ptrace_attach
	https://lore.kernel.org/all/20231117094531.GN8262@noisy.programming.kicks-ass.net/

Oleg.

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: test
Author: danielyangkang@gmail.com

#syz test

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: test
Author: danielyangkang@gmail.com

#syz test

Re: [syzbot] Test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test 

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git dccb07f2914cdab2ac3a5b6c98406f765acab803

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] Test

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git fe46a7dd189e25604716c03576d05ac8a5209743

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] test

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Author: mukattreyee@gmail.com

#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

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Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 71b1543c83d65af8215d7558d70fc2ecbee77dcf

---
 net/sched/sch_taprio.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index a0d54b422186..41add4a1d407 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -44,6 +44,8 @@ static struct static_key_false taprio_have_working_mqprio;
 	(TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST | TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
 #define TAPRIO_FLAGS_INVALID U32_MAX
 
+#define TAPRIO_MAX_NUM_SCHEDULES_BEFORE_NOW 10
+
 struct sched_entry {
 	/* Durations between this GCL entry and the GCL entry where the
 	 * respective traffic class gate closes
@@ -62,6 +64,8 @@ struct sched_entry {
 	u32 gate_mask;
 	u32 interval;
 	u8 command;
+	/* Used to skip some cycles to prevent other tasks from starving */
+	u8 num_schedules_before_now;
 };
 
 struct sched_gate_list {
@@ -111,6 +115,9 @@ struct __tc_taprio_qopt_offload {
 	struct tc_taprio_qopt_offload offload;
 };
 
+static void setup_txtime(struct taprio_sched *q,
+			 struct sched_gate_list *sched, ktime_t base);
+
 static void taprio_calculate_gate_durations(struct taprio_sched *q,
 					    struct sched_gate_list *sched)
 {
@@ -919,6 +926,7 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 	struct sched_entry *entry, *next;
 	struct Qdisc *sch = q->root;
 	ktime_t end_time;
+	ktime_t basenow;
 	int tc;
 
 	spin_lock(&q->current_entry_lock);
@@ -977,6 +985,23 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 	taprio_set_budgets(q, oper, next);
 
 first_run:
+	basenow = ktime_get();
+	if (ktime_before(end_time, basenow))
+	{
+		next->num_schedules_before_now++;
+		if (next->num_schedules_before_now >= TAPRIO_MAX_NUM_SCHEDULES_BEFORE_NOW)
+		{
+			end_time = ktime_add_ns(basenow, oper->cycle_time);
+			next->end_time = end_time;
+			next->num_schedules_before_now = 0;
+			setup_txtime(q, oper, basenow);
+		}
+	}
+	else
+	{
+		next->num_schedules_before_now = 0;
+	}
+
 	rcu_assign_pointer(q->current_entry, next);
 	spin_unlock(&q->current_entry_lock);
 
@@ -1074,6 +1099,7 @@ static int parse_sched_entry(struct taprio_sched *q, struct nlattr *n,
 	}
 
 	entry->index = index;
+	entry->num_schedules_before_now = 0;
 
 	return fill_sched_entry(q, tb, entry, extack);
 }
-- 
2.43.0

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Author: ghandatmanas@gmail.com

#syz test: 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: test
Author: ghandatmanas@gmail.com

#syz test: 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: test
Author: ghandatmanas@gmail.com

#syz test: 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master