[syzbot] [mm?] [arch?] BUG: sleeping function called from invalid context in __tlb_batch_free_encoded_pages

[syzbot] [mm?] [arch?] BUG: sleeping function called from invalid context in __tlb_batch_free_encoded_pages

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    dca922e019dd Merge tag 'xsa48x-7.1-tag' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11cd6b6c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=59da38148f3a3d24
dashboard link: https://syzkaller.appspot.com/bug?extid=a169a27b0538ba43e5d3
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-dca922e0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7b447b1b93a9/vmlinux-dca922e0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/af7830f5dabf/bzImage-dca922e0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a169a27b0538ba43e5d3@syzkaller.appspotmail.com

BUG: sleeping function called from invalid context at mm/mmu_gather.c:142
in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 5677, name: rm
preempt_count: 0, expected: 0
RCU nest depth: 1, expected: 0
2 locks held by rm/5677:
 #0: ffff888022c20338 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock include/linux/mmap_lock.h:536 [inline]
 #0: ffff888022c20338 (&mm->mmap_lock){++++}-{4:4}, at: exit_mmap+0x22c/0xa10 mm/mmap.c:1308
 #1: ffffffff8e7e54e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire.constprop.0+0x7/0x30 include/linux/rcupdate.h:300
CPU: 1 UID: 0 PID: 5677 Comm: rm Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 __might_resched.cold+0x1ec/0x232 kernel/sched/core.c:9162
 __tlb_batch_free_encoded_pages+0x11e/0x280 mm/mmu_gather.c:142
 tlb_batch_pages_flush mm/mmu_gather.c:151 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:417 [inline]
 tlb_flush_mmu mm/mmu_gather.c:424 [inline]
 tlb_finish_mmu+0x1b0/0x810 mm/mmu_gather.c:549
 exit_mmap+0x454/0xa10 mm/mmap.c:1313
 __mmput+0x12a/0x410 kernel/fork.c:1178
 mmput+0x67/0x80 kernel/fork.c:1201
 exit_mm kernel/exit.c:581 [inline]
 do_exit+0x833/0x2a60 kernel/exit.c:963
 do_group_exit+0xd5/0x2a0 kernel/exit.c:1117
 __do_sys_exit_group kernel/exit.c:1128 [inline]
 __se_sys_exit_group kernel/exit.c:1126 [inline]
 __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1126
 x64_sys_call+0x102c/0x1530 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9fc102d6c5
Code: Unable to access opcode bytes at 0x7f9fc102d69b.
RSP: 002b:00007ffd51104bf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f9fc112efe8 RCX: 00007f9fc102d6c5
RDX: 00000000000000e7 RSI: ffffffffffffff88 RDI: 0000000000000000
RBP: 0000000000000001 R08: 00007ffd51104b88 R09: 0000000000000000
R10: 00007ffd51104a20 R11: 0000000000000202 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f9fc112d680 R15: 00007f9fc112f000
 </TASK>

====================================
WARNING: rm/5677 still has locks held!
syzkaller #0 Tainted: G        W          
------------------------------------
1 lock held by rm/5677:
 #0: ffffffff8e7e54e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire.constprop.0+0x7/0x30 include/linux/rcupdate.h:300

stack backtrace:
CPU: 1 UID: 0 PID: 5677 Comm: rm Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_held_locks_bug kernel/locking/lockdep.c:6752 [inline]
 debug_check_no_locks_held+0x90/0xa0 kernel/locking/lockdep.c:6760
 do_exit+0x13ea/0x2a60 kernel/exit.c:997
 do_group_exit+0xd5/0x2a0 kernel/exit.c:1117
 __do_sys_exit_group kernel/exit.c:1128 [inline]
 __se_sys_exit_group kernel/exit.c:1126 [inline]
 __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1126
 x64_sys_call+0x102c/0x1530 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9fc102d6c5
Code: Unable to access opcode bytes at 0x7f9fc102d69b.
RSP: 002b:00007ffd51104bf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f9fc112efe8 RCX: 00007f9fc102d6c5
RDX: 00000000000000e7 RSI: ffffffffffffff88 RDI: 0000000000000000
RBP: 0000000000000001 R08: 00007ffd51104b88 R09: 0000000000000000
R10: 00007ffd51104a20 R11: 0000000000000202 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f9fc112d680 R15: 00007f9fc112f000
 </TASK>


---
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#syz undup

Re: [syzbot] [mm?] [arch?] BUG: sleeping function called from invalid context in __tlb_batch_free_encoded_pages

[Will Deacon]

I finally got a chance to look at this one...

On Thu, Apr 30, 2026 at 12:21:35AM -0700, syzbot wrote:
> syzbot found the following issue on:
> 
> HEAD commit:    dca922e019dd Merge tag 'xsa48x-7.1-tag' of git://git.kerne..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11cd6b6c580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=59da38148f3a3d24
> dashboard link: https://syzkaller.appspot.com/bug?extid=a169a27b0538ba43e5d3
> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-dca922e0.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/7b447b1b93a9/vmlinux-dca922e0.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/af7830f5dabf/bzImage-dca922e0.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a169a27b0538ba43e5d3@syzkaller.appspotmail.com
> 
> BUG: sleeping function called from invalid context at mm/mmu_gather.c:142
> in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 5677, name: rm
> preempt_count: 0, expected: 0
> RCU nest depth: 1, expected: 0
> 2 locks held by rm/5677:
>  #0: ffff888022c20338 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock include/linux/mmap_lock.h:536 [inline]
>  #0: ffff888022c20338 (&mm->mmap_lock){++++}-{4:4}, at: exit_mmap+0x22c/0xa10 mm/mmap.c:1308
>  #1: ffffffff8e7e54e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire.constprop.0+0x7/0x30 include/linux/rcupdate.h:300
> CPU: 1 UID: 0 PID: 5677 Comm: rm Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
>  __might_resched.cold+0x1ec/0x232 kernel/sched/core.c:9162
>  __tlb_batch_free_encoded_pages+0x11e/0x280 mm/mmu_gather.c:142
>  tlb_batch_pages_flush mm/mmu_gather.c:151 [inline]

... so we're getting deep in the gather code tearing down an mm, where
we free the unmapped pages but we're somehow inside an RCU read-side
critical section.

The last report on the sysbot dashboard is from 30th April, which
coincides with 99ebc509eef5 ("mm: memcontrol: fix rcu unbalance in
get_non_dying_memcg_end()") landing upstream. Unfortunately, there's no
reproducer available to test that concretely but it looks like we can
end up in there via the page freeing path. So hopefully this is fixed.

As an aside, it's a bit of a pity that the rcu_read_lock() callsite is
identified only as the useless rcu_lock_acquire.constprop.0() function
in this backtrace.

Will

>  tlb_flush_mmu_free mm/mmu_gather.c:417 [inline]
>  tlb_flush_mmu mm/mmu_gather.c:424 [inline]
>  tlb_finish_mmu+0x1b0/0x810 mm/mmu_gather.c:549
>  exit_mmap+0x454/0xa10 mm/mmap.c:1313
>  __mmput+0x12a/0x410 kernel/fork.c:1178
>  mmput+0x67/0x80 kernel/fork.c:1201
>  exit_mm kernel/exit.c:581 [inline]
>  do_exit+0x833/0x2a60 kernel/exit.c:963
>  do_group_exit+0xd5/0x2a0 kernel/exit.c:1117
>  __do_sys_exit_group kernel/exit.c:1128 [inline]
>  __se_sys_exit_group kernel/exit.c:1126 [inline]
>  __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1126
>  x64_sys_call+0x102c/0x1530 arch/x86/include/generated/asm/syscalls_64.h:232
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f9fc102d6c5
> Code: Unable to access opcode bytes at 0x7f9fc102d69b.
> RSP: 002b:00007ffd51104bf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 00007f9fc112efe8 RCX: 00007f9fc102d6c5
> RDX: 00000000000000e7 RSI: ffffffffffffff88 RDI: 0000000000000000
> RBP: 0000000000000001 R08: 00007ffd51104b88 R09: 0000000000000000
> R10: 00007ffd51104a20 R11: 0000000000000202 R12: 0000000000000000
> R13: 0000000000000000 R14: 00007f9fc112d680 R15: 00007f9fc112f000
>  </TASK>
> 
> ====================================
> WARNING: rm/5677 still has locks held!
> syzkaller #0 Tainted: G        W          
> ------------------------------------
> 1 lock held by rm/5677:
>  #0: ffffffff8e7e54e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire.constprop.0+0x7/0x30 include/linux/rcupdate.h:300
> 
> stack backtrace:
> CPU: 1 UID: 0 PID: 5677 Comm: rm Tainted: G        W           syzkaller #0 PREEMPT(full) 
> Tainted: [W]=WARN
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
>  print_held_locks_bug kernel/locking/lockdep.c:6752 [inline]
>  debug_check_no_locks_held+0x90/0xa0 kernel/locking/lockdep.c:6760
>  do_exit+0x13ea/0x2a60 kernel/exit.c:997
>  do_group_exit+0xd5/0x2a0 kernel/exit.c:1117
>  __do_sys_exit_group kernel/exit.c:1128 [inline]
>  __se_sys_exit_group kernel/exit.c:1126 [inline]
>  __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1126
>  x64_sys_call+0x102c/0x1530 arch/x86/include/generated/asm/syscalls_64.h:232
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f9fc102d6c5
> Code: Unable to access opcode bytes at 0x7f9fc102d69b.
> RSP: 002b:00007ffd51104bf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 00007f9fc112efe8 RCX: 00007f9fc102d6c5
> RDX: 00000000000000e7 RSI: ffffffffffffff88 RDI: 0000000000000000
> RBP: 0000000000000001 R08: 00007ffd51104b88 R09: 0000000000000000
> R10: 00007ffd51104a20 R11: 0000000000000202 R12: 0000000000000000
> R13: 0000000000000000 R14: 00007f9fc112d680 R15: 00007f9fc112f000
>  </TASK>
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup

Re: [syzbot] [mm?] [arch?] BUG: sleeping function called from invalid context in __tlb_batch_free_encoded_pages

[David Hildenbrand (Arm)]

On 5/27/26 14:05, Will Deacon wrote:
> I finally got a chance to look at this one...
> 
> On Thu, Apr 30, 2026 at 12:21:35AM -0700, syzbot wrote:
>> syzbot found the following issue on:
>>
>> HEAD commit:    dca922e019dd Merge tag 'xsa48x-7.1-tag' of git://git.kerne..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=11cd6b6c580000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=59da38148f3a3d24
>> dashboard link: https://syzkaller.appspot.com/bug?extid=a169a27b0538ba43e5d3
>> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
>>
>> Unfortunately, I don't have any reproducer for this issue yet.
>>
>> Downloadable assets:
>> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-dca922e0.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/7b447b1b93a9/vmlinux-dca922e0.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/af7830f5dabf/bzImage-dca922e0.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+a169a27b0538ba43e5d3@syzkaller.appspotmail.com
>>
>> BUG: sleeping function called from invalid context at mm/mmu_gather.c:142
>> in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 5677, name: rm
>> preempt_count: 0, expected: 0
>> RCU nest depth: 1, expected: 0
>> 2 locks held by rm/5677:
>>  #0: ffff888022c20338 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock include/linux/mmap_lock.h:536 [inline]
>>  #0: ffff888022c20338 (&mm->mmap_lock){++++}-{4:4}, at: exit_mmap+0x22c/0xa10 mm/mmap.c:1308
>>  #1: ffffffff8e7e54e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire.constprop.0+0x7/0x30 include/linux/rcupdate.h:300
>> CPU: 1 UID: 0 PID: 5677 Comm: rm Not tainted syzkaller #0 PREEMPT(full) 
>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
>> Call Trace:
>>  <TASK>
>>  __dump_stack lib/dump_stack.c:94 [inline]
>>  dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
>>  __might_resched.cold+0x1ec/0x232 kernel/sched/core.c:9162
>>  __tlb_batch_free_encoded_pages+0x11e/0x280 mm/mmu_gather.c:142
>>  tlb_batch_pages_flush mm/mmu_gather.c:151 [inline]
> 
> ... so we're getting deep in the gather code tearing down an mm, where
> we free the unmapped pages but we're somehow inside an RCU read-side
> critical section.
> 
> The last report on the sysbot dashboard is from 30th April, which
> coincides with 99ebc509eef5 ("mm: memcontrol: fix rcu unbalance in
> get_non_dying_memcg_end()") landing upstream. Unfortunately, there's no
> reproducer available to test that concretely but it looks like we can
> end up in there via the page freeing path. So hopefully this is fixed.

Yes, sounds reasonable.

-- 
Cheers,

David