* [syzbot] [kvm?] WARNING: locking bug in __refill_objects_node
@ 2026-10-26 10:19 syzbot
2026-10-26 22:43 ` Hillf Danton
0 siblings, 1 reply; 4+ messages in thread
From: syzbot @ 2026-10-26 10:19 UTC (permalink / raw)
To: kvm, linux-kernel, syzkaller-bugs
Hello,
syzbot found the following issue on:
HEAD commit: c03c1a14507d Linux 7.3
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=128d8ca5580000
kernel config: https://syzkaller.appspot.com/x/.config?x=129d675874dbf896
dashboard link: https://syzkaller.appspot.com/bug?extid=f11512d1e5878ba5e60e
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=168d8ca5580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f11512d1e5878ba5e60e@syzkaller.appspotmail.com
=============================
[ BUG: Invalid wait context ]
syzkaller #0 Tainted: G S
-----------------------------
syz-executor177/6041 is trying to lock:
ffff88801d040618 (&n->list_lock){-.-.}-{3:3}, at: get_partial_node_bulk mm/slub.c:3831 [inline]
ffff88801d040618 (&n->list_lock){-.-.}-{3:3}, at: __refill_objects_node+0x104/0xab0 mm/slub.c:7279
other info that might help us debug this:
context-{2:2}
locks held by syz-executor177/6041: 1, last CPU#1:
#0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:198 [inline]
#0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:305 [inline]
#0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: tomoyo_read_lock security/tomoyo/common.h:1112 [inline]
#0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: tomoyo_check_open_permission+0x169/0x3c0 security/tomoyo/file.c:772
stack backtrace:
CPU: 1 UID: 0 PID: 6041 Comm: syz-executor177 Tainted: G S syzkaller #0 PREEMPT(full)
Tainted: [S]=CPU_OUT_OF_SPEC
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_lock_invalid_wait_context kernel/locking/lockdep.c:4874 [inline]
check_wait_context kernel/locking/lockdep.c:4946 [inline]
__lock_acquire+0xfcc/0x1f40 kernel/locking/lockdep.c:5238
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:155 [inline]
_raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:181
get_partial_node_bulk mm/slub.c:3831 [inline]
__refill_objects_node+0x104/0xab0 mm/slub.c:7279
refill_objects+0x58/0x410 mm/slub.c:7405
refill_sheaf mm/slub.c:2885 [inline]
__pcs_replace_empty_main+0x35e/0x650 mm/slub.c:4774
alloc_from_pcs mm/slub.c:4850 [inline]
slab_alloc_node mm/slub.c:4984 [inline]
__kmalloc_cache_noprof+0x4f4/0x6d0 mm/slub.c:5559
_kmalloc_noprof include/linux/slab.h:991 [inline]
_kzalloc_noprof include/linux/slab.h:1312 [inline]
kvm_async_pf_task_wake arch/x86/kernel/kvm.c:224 [inline]
__sysvec_kvm_asyncpf_interrupt+0x334/0x610 arch/x86/kernel/kvm.c:338
instr_sysvec_kvm_asyncpf_interrupt arch/x86/kernel/kvm.c:327 [inline]
sysvec_kvm_asyncpf_interrupt+0x9e/0xc0 arch/x86/kernel/kvm.c:327
</IRQ>
<TASK>
asm_sysvec_kvm_asyncpf_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:753
RIP: 0010:memcmp+0x156/0x1d0 lib/string.c:665
Code: 0f 86 fb fe ff ff 48 89 d8 48 89 de 48 c1 e8 03 83 e6 07 42 0f b6 14 28 48 8d 43 07 48 89 c1 48 c1 e9 03 40 38 f2 40 0f 9e c6 <84> d2 42 0f b6 0c 29 0f 95 c2 40 84 d6 0f 84 45 ff ff ff be 08 00
RSP: 0018:ffffc90003ab7538 EFLAGS: 00000297
RAX: ffff8880220be413 RBX: ffff8880220be40c RCX: 1ffff11004417c82
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8880220be40c
RBP: ffffffff8c58a940 R08: 0000000000000001 R09: 0000000000000066
R10: 0000000000000066 R11: 0000000000000001 R12: 0000000000000012
R13: dffffc0000000000 R14: dffffc0000000000 R15: 0000000000000000
strstr+0x109/0x170 lib/string.c:743
tomoyo_add_entry security/tomoyo/common.c:2157 [inline]
tomoyo_supervisor+0xf47/0x1340 security/tomoyo/common.c:2238
tomoyo_audit_path_log security/tomoyo/file.c:169 [inline]
tomoyo_path_permission security/tomoyo/file.c:592 [inline]
tomoyo_path_permission+0x270/0x3b0 security/tomoyo/file.c:577
tomoyo_check_open_permission+0x37f/0x3c0 security/tomoyo/file.c:782
tomoyo_file_open+0x6b/0x90 security/tomoyo/tomoyo.c:334
security_file_open+0xb5/0x1e0 security/security.c:2739
do_dentry_open+0x588/0x14d0 fs/open.c:973
vfs_open+0x82/0x3f0 fs/open.c:1101
do_open fs/namei.c:4836 [inline]
path_openat+0x1a23/0x2450 fs/namei.c:4999
do_file_open+0x20e/0x430 fs/namei.c:5028
do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
do_sys_open fs/open.c:1423 [inline]
__do_sys_openat fs/open.c:1439 [inline]
__se_sys_openat fs/open.c:1434 [inline]
__x64_sys_openat+0x12d/0x210 fs/open.c:1434
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f589f9da7be
Code: 08 0f 85 55 ec ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 90 41 57 41 56 4d 89 c6 41 55 4d 89 cd 41 54 55 53 48 83 ec 08
RSP: 002b:00007f589affe098 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f589affe6c0 RCX: 00007f589f9da7be
RDX: 0000000000000002 RSI: 00007f589affe1a0 RDI: ffffffffffffff9c
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f589affe1a0
R13: 0000000000000001 R14: 00007ffef59973a0 R15: 00007ffef5997488
</TASK>
----------------
Code disassembly (best guess):
0: 0f 86 fb fe ff ff jbe 0xffffff01
6: 48 89 d8 mov %rbx,%rax
9: 48 89 de mov %rbx,%rsi
c: 48 c1 e8 03 shr $0x3,%rax
10: 83 e6 07 and $0x7,%esi
13: 42 0f b6 14 28 movzbl (%rax,%r13,1),%edx
18: 48 8d 43 07 lea 0x7(%rbx),%rax
1c: 48 89 c1 mov %rax,%rcx
1f: 48 c1 e9 03 shr $0x3,%rcx
23: 40 38 f2 cmp %sil,%dl
26: 40 0f 9e c6 setle %sil
* 2a: 84 d2 test %dl,%dl <-- trapping instruction
2c: 42 0f b6 0c 29 movzbl (%rcx,%r13,1),%ecx
31: 0f 95 c2 setne %dl
34: 40 84 d6 test %dl,%sil
37: 0f 84 45 ff ff ff je 0xffffff82
3d: be .byte 0xbe
3e: 08 00 or %al,(%rax)
---
This report is generated by a bot. It may contain errors.
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [syzbot] [kvm?] WARNING: locking bug in __refill_objects_node
2026-10-26 10:19 [syzbot] [kvm?] WARNING: locking bug in __refill_objects_node syzbot
@ 2026-10-26 22:43 ` Hillf Danton
2026-10-27 14:00 ` Sean Christopherson
0 siblings, 1 reply; 4+ messages in thread
From: Hillf Danton @ 2026-10-26 22:43 UTC (permalink / raw)
To: Boqun Feng; +Cc: syzbot, kvm, linux-kernel, Tetsuo Handa, syzkaller-bugs
Ask the locking people to shed light on the warning.
> Date: Mon, 26 Oct 2026 03:19:37 -0700 [thread overview]
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: c03c1a14507d Linux 7.3
> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=128d8ca5580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=129d675874dbf896
> dashboard link: https://syzkaller.appspot.com/bug?extid=f11512d1e5878ba5e60e
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=168d8ca5580000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+f11512d1e5878ba5e60e@syzkaller.appspotmail.com
>
> =============================
> [ BUG: Invalid wait context ]
> syzkaller #0 Tainted: G S
> -----------------------------
> syz-executor177/6041 is trying to lock:
> ffff88801d040618 (&n->list_lock){-.-.}-{3:3}, at: get_partial_node_bulk mm/slub.c:3831 [inline]
> ffff88801d040618 (&n->list_lock){-.-.}-{3:3}, at: __refill_objects_node+0x104/0xab0 mm/slub.c:7279
> other info that might help us debug this:
> context-{2:2}
> locks held by syz-executor177/6041: 1, last CPU#1:
> #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:198 [inline]
> #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:305 [inline]
> #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: tomoyo_read_lock security/tomoyo/common.h:1112 [inline]
> #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: tomoyo_check_open_permission+0x169/0x3c0 security/tomoyo/file.c:772
> stack backtrace:
> CPU: 1 UID: 0 PID: 6041 Comm: syz-executor177 Tainted: G S syzkaller #0 PREEMPT(full)
> Tainted: [S]=CPU_OUT_OF_SPEC
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> Call Trace:
> <IRQ>
> __dump_stack lib/dump_stack.c:94 [inline]
> dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
> print_lock_invalid_wait_context kernel/locking/lockdep.c:4874 [inline]
> check_wait_context kernel/locking/lockdep.c:4946 [inline]
> __lock_acquire+0xfcc/0x1f40 kernel/locking/lockdep.c:5238
> lock_acquire kernel/locking/lockdep.c:5942 [inline]
> lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:155 [inline]
> _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:181
> get_partial_node_bulk mm/slub.c:3831 [inline]
> __refill_objects_node+0x104/0xab0 mm/slub.c:7279
> refill_objects+0x58/0x410 mm/slub.c:7405
> refill_sheaf mm/slub.c:2885 [inline]
> __pcs_replace_empty_main+0x35e/0x650 mm/slub.c:4774
> alloc_from_pcs mm/slub.c:4850 [inline]
> slab_alloc_node mm/slub.c:4984 [inline]
> __kmalloc_cache_noprof+0x4f4/0x6d0 mm/slub.c:5559
> _kmalloc_noprof include/linux/slab.h:991 [inline]
> _kzalloc_noprof include/linux/slab.h:1312 [inline]
> kvm_async_pf_task_wake arch/x86/kernel/kvm.c:224 [inline]
> __sysvec_kvm_asyncpf_interrupt+0x334/0x610 arch/x86/kernel/kvm.c:338
> instr_sysvec_kvm_asyncpf_interrupt arch/x86/kernel/kvm.c:327 [inline]
> sysvec_kvm_asyncpf_interrupt+0x9e/0xc0 arch/x86/kernel/kvm.c:327
> </IRQ>
> <TASK>
> asm_sysvec_kvm_asyncpf_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:753
> RIP: 0010:memcmp+0x156/0x1d0 lib/string.c:665
> Code: 0f 86 fb fe ff ff 48 89 d8 48 89 de 48 c1 e8 03 83 e6 07 42 0f b6 14 28 48 8d 43 07 48 89 c1 48 c1 e9 03 40 38 f2 40 0f 9e c6 <84> d2 42 0f b6 0c 29 0f 95 c2 40 84 d6 0f 84 45 ff ff ff be 08 00
> RSP: 0018:ffffc90003ab7538 EFLAGS: 00000297
> RAX: ffff8880220be413 RBX: ffff8880220be40c RCX: 1ffff11004417c82
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8880220be40c
> RBP: ffffffff8c58a940 R08: 0000000000000001 R09: 0000000000000066
> R10: 0000000000000066 R11: 0000000000000001 R12: 0000000000000012
> R13: dffffc0000000000 R14: dffffc0000000000 R15: 0000000000000000
> strstr+0x109/0x170 lib/string.c:743
> tomoyo_add_entry security/tomoyo/common.c:2157 [inline]
> tomoyo_supervisor+0xf47/0x1340 security/tomoyo/common.c:2238
> tomoyo_audit_path_log security/tomoyo/file.c:169 [inline]
> tomoyo_path_permission security/tomoyo/file.c:592 [inline]
> tomoyo_path_permission+0x270/0x3b0 security/tomoyo/file.c:577
> tomoyo_check_open_permission+0x37f/0x3c0 security/tomoyo/file.c:782
> tomoyo_file_open+0x6b/0x90 security/tomoyo/tomoyo.c:334
> security_file_open+0xb5/0x1e0 security/security.c:2739
> do_dentry_open+0x588/0x14d0 fs/open.c:973
> vfs_open+0x82/0x3f0 fs/open.c:1101
> do_open fs/namei.c:4836 [inline]
> path_openat+0x1a23/0x2450 fs/namei.c:4999
> do_file_open+0x20e/0x430 fs/namei.c:5028
> do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
> do_sys_open fs/open.c:1423 [inline]
> __do_sys_openat fs/open.c:1439 [inline]
> __se_sys_openat fs/open.c:1434 [inline]
> __x64_sys_openat+0x12d/0x210 fs/open.c:1434
> do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
> do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [syzbot] [kvm?] WARNING: locking bug in __refill_objects_node
2026-10-26 22:43 ` Hillf Danton
@ 2026-10-27 14:00 ` Sean Christopherson
2026-10-27 18:48 ` Harry Yoo
0 siblings, 1 reply; 4+ messages in thread
From: Sean Christopherson @ 2026-10-27 14:00 UTC (permalink / raw)
To: Hillf Danton
Cc: Boqun Feng, syzbot, kvm, linux-kernel, Tetsuo Handa,
syzkaller-bugs, Vlastimil Babka, Harry Yoo, Andrew Morton,
Hao Li, Christoph Lameter, David Rientjes, Roman Gushchin,
linux-mm
+slub folks
On Tue, Oct 27, 2026, Hillf Danton wrote:
> Ask the locking people to shed light on the warning.
get_partial_node_bulk() is waiting on a non-raw spinlock while in hard IRQ context,
and it looks like __refill_objects_node() would do the same later on. On PREEMPT_RT,
those spinlocks become sleepable locks, which is what triggers the splat.
The alloction coming from KVM-as-a-guest code is GFP_ATOMIC, so I think that wonky
code is fine.
> > Date: Mon, 26 Oct 2026 03:19:37 -0700 [thread overview]
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: c03c1a14507d Linux 7.3
> > git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > console output: https://syzkaller.appspot.com/x/log.txt?x=128d8ca5580000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=129d675874dbf896
> > dashboard link: https://syzkaller.appspot.com/bug?extid=f11512d1e5878ba5e60e
> > compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=168d8ca5580000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+f11512d1e5878ba5e60e@syzkaller.appspotmail.com
> >
> > =============================
> > [ BUG: Invalid wait context ]
> > syzkaller #0 Tainted: G S
> > -----------------------------
> > syz-executor177/6041 is trying to lock:
> > ffff88801d040618 (&n->list_lock){-.-.}-{3:3}, at: get_partial_node_bulk mm/slub.c:3831 [inline]
> > ffff88801d040618 (&n->list_lock){-.-.}-{3:3}, at: __refill_objects_node+0x104/0xab0 mm/slub.c:7279
> > other info that might help us debug this:
> > context-{2:2}
> > locks held by syz-executor177/6041: 1, last CPU#1:
> > #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:198 [inline]
> > #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:305 [inline]
> > #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: tomoyo_read_lock security/tomoyo/common.h:1112 [inline]
> > #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: tomoyo_check_open_permission+0x169/0x3c0 security/tomoyo/file.c:772
> > stack backtrace:
> > CPU: 1 UID: 0 PID: 6041 Comm: syz-executor177 Tainted: G S syzkaller #0 PREEMPT(full)
> > Tainted: [S]=CPU_OUT_OF_SPEC
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> > Call Trace:
> > <IRQ>
> > __dump_stack lib/dump_stack.c:94 [inline]
> > dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
> > print_lock_invalid_wait_context kernel/locking/lockdep.c:4874 [inline]
> > check_wait_context kernel/locking/lockdep.c:4946 [inline]
> > __lock_acquire+0xfcc/0x1f40 kernel/locking/lockdep.c:5238
> > lock_acquire kernel/locking/lockdep.c:5942 [inline]
> > lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
> > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:155 [inline]
> > _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:181
> > get_partial_node_bulk mm/slub.c:3831 [inline]
> > __refill_objects_node+0x104/0xab0 mm/slub.c:7279
> > refill_objects+0x58/0x410 mm/slub.c:7405
> > refill_sheaf mm/slub.c:2885 [inline]
> > __pcs_replace_empty_main+0x35e/0x650 mm/slub.c:4774
> > alloc_from_pcs mm/slub.c:4850 [inline]
> > slab_alloc_node mm/slub.c:4984 [inline]
> > __kmalloc_cache_noprof+0x4f4/0x6d0 mm/slub.c:5559
> > _kmalloc_noprof include/linux/slab.h:991 [inline]
> > _kzalloc_noprof include/linux/slab.h:1312 [inline]
> > kvm_async_pf_task_wake arch/x86/kernel/kvm.c:224 [inline]
> > __sysvec_kvm_asyncpf_interrupt+0x334/0x610 arch/x86/kernel/kvm.c:338
> > instr_sysvec_kvm_asyncpf_interrupt arch/x86/kernel/kvm.c:327 [inline]
> > sysvec_kvm_asyncpf_interrupt+0x9e/0xc0 arch/x86/kernel/kvm.c:327
> > </IRQ>
> > <TASK>
> > asm_sysvec_kvm_asyncpf_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:753
> > RIP: 0010:memcmp+0x156/0x1d0 lib/string.c:665
> > Code: 0f 86 fb fe ff ff 48 89 d8 48 89 de 48 c1 e8 03 83 e6 07 42 0f b6 14 28 48 8d 43 07 48 89 c1 48 c1 e9 03 40 38 f2 40 0f 9e c6 <84> d2 42 0f b6 0c 29 0f 95 c2 40 84 d6 0f 84 45 ff ff ff be 08 00
> > RSP: 0018:ffffc90003ab7538 EFLAGS: 00000297
> > RAX: ffff8880220be413 RBX: ffff8880220be40c RCX: 1ffff11004417c82
> > RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8880220be40c
> > RBP: ffffffff8c58a940 R08: 0000000000000001 R09: 0000000000000066
> > R10: 0000000000000066 R11: 0000000000000001 R12: 0000000000000012
> > R13: dffffc0000000000 R14: dffffc0000000000 R15: 0000000000000000
> > strstr+0x109/0x170 lib/string.c:743
> > tomoyo_add_entry security/tomoyo/common.c:2157 [inline]
> > tomoyo_supervisor+0xf47/0x1340 security/tomoyo/common.c:2238
> > tomoyo_audit_path_log security/tomoyo/file.c:169 [inline]
> > tomoyo_path_permission security/tomoyo/file.c:592 [inline]
> > tomoyo_path_permission+0x270/0x3b0 security/tomoyo/file.c:577
> > tomoyo_check_open_permission+0x37f/0x3c0 security/tomoyo/file.c:782
> > tomoyo_file_open+0x6b/0x90 security/tomoyo/tomoyo.c:334
> > security_file_open+0xb5/0x1e0 security/security.c:2739
> > do_dentry_open+0x588/0x14d0 fs/open.c:973
> > vfs_open+0x82/0x3f0 fs/open.c:1101
> > do_open fs/namei.c:4836 [inline]
> > path_openat+0x1a23/0x2450 fs/namei.c:4999
> > do_file_open+0x20e/0x430 fs/namei.c:5028
> > do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
> > do_sys_open fs/open.c:1423 [inline]
> > __do_sys_openat fs/open.c:1439 [inline]
> > __se_sys_openat fs/open.c:1434 [inline]
> > __x64_sys_openat+0x12d/0x210 fs/open.c:1434
> > do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
> > do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [syzbot] [kvm?] WARNING: locking bug in __refill_objects_node
2026-10-27 14:00 ` Sean Christopherson
@ 2026-10-27 18:48 ` Harry Yoo
0 siblings, 0 replies; 4+ messages in thread
From: Harry Yoo @ 2026-10-27 18:48 UTC (permalink / raw)
To: Sean Christopherson
Cc: Hillf Danton, Boqun Feng, syzbot, kvm, linux-kernel,
Tetsuo Handa, syzkaller-bugs, Vlastimil Babka, Andrew Morton,
Hao Li, Christoph Lameter, David Rientjes, Roman Gushchin,
linux-mm, Sebastian Andrzej Siewior, Clark Williams,
Steven Rostedt, linux-rt-devel
[+Cc RT folks]
On Tue, Oct 27, 2026 at 07:00:16AM -0700, Sean Christopherson wrote:
> +slub folks
>
> On Tue, Oct 27, 2026, Hillf Danton wrote:
> > Ask the locking people to shed light on the warning.
>
> get_partial_node_bulk() is waiting on a non-raw spinlock while in hard IRQ context,
> and it looks like __refill_objects_node() would do the same later on. On PREEMPT_RT,
> those spinlocks become sleepable locks, which is what triggers the splat.
>
> The alloction coming from KVM-as-a-guest code is GFP_ATOMIC, so I think that wonky
> code is fine.
But memory allocation w/ GFP_ATOMIC is fine only on non-RT?
From the documentation:
https://docs.kernel.org/core-api/real-time/differences.html#memory-allocation
> The memory allocation APIs, such as kmalloc() and alloc_pages(),
> require a gfp_t flag to indicate the allocation context.
> On non-PREEMPT_RT kernels, it is necessary to use GFP_ATOMIC when
> allocating memory from interrupt context or from sections where
> preemption is disabled. This is because the allocator must not
> sleep in these contexts waiting for memory to become available.
Here it mentions GFP_ATOMIC allocations in preemption disabled
contexts on non-RT, and...
> However, this approach does not work on PREEMPT_RT kernels.
> The memory allocator in PREEMPT_RT uses sleeping locks internally,
> which cannot be acquired when preemption is disabled.
it says we shoud not allocate memory in such a context on RT?
> Fortunately,
> this is generally not a problem, because PREEMPT_RT moves most contexts
> that would traditionally run with preemption or interrupts disabled
> into threaded context, where sleeping is allowed.
Not sure if this applies here as I don't understand what's
going in in KVM world.
> > > Date: Mon, 26 Oct 2026 03:19:37 -0700 [thread overview]
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit: c03c1a14507d Linux 7.3
> > > git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=128d8ca5580000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=129d675874dbf896
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=f11512d1e5878ba5e60e
> > > compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=168d8ca5580000
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+f11512d1e5878ba5e60e@syzkaller.appspotmail.com
> > >
> > > =============================
> > > [ BUG: Invalid wait context ]
> > > syzkaller #0 Tainted: G S
> > > -----------------------------
> > > syz-executor177/6041 is trying to lock:
> > > ffff88801d040618 (&n->list_lock){-.-.}-{3:3}, at: get_partial_node_bulk mm/slub.c:3831 [inline]
> > > ffff88801d040618 (&n->list_lock){-.-.}-{3:3}, at: __refill_objects_node+0x104/0xab0 mm/slub.c:7279
> > > other info that might help us debug this:
> > > context-{2:2}
> > > locks held by syz-executor177/6041: 1, last CPU#1:
> > > #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:198 [inline]
> > > #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:305 [inline]
> > > #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: tomoyo_read_lock security/tomoyo/common.h:1112 [inline]
> > > #0: ffffffff9090b438 (tomoyo_ss){.+.+}-{0:0}, at: tomoyo_check_open_permission+0x169/0x3c0 security/tomoyo/file.c:772
> > > stack backtrace:
> > > CPU: 1 UID: 0 PID: 6041 Comm: syz-executor177 Tainted: G S syzkaller #0 PREEMPT(full)
> > > Tainted: [S]=CPU_OUT_OF_SPEC
> > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> > > Call Trace:
> > > <IRQ>
> > > __dump_stack lib/dump_stack.c:94 [inline]
> > > dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
> > > print_lock_invalid_wait_context kernel/locking/lockdep.c:4874 [inline]
> > > check_wait_context kernel/locking/lockdep.c:4946 [inline]
> > > __lock_acquire+0xfcc/0x1f40 kernel/locking/lockdep.c:5238
> > > lock_acquire kernel/locking/lockdep.c:5942 [inline]
> > > lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
> > > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:155 [inline]
> > > _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:181
> > > get_partial_node_bulk mm/slub.c:3831 [inline]
> > > __refill_objects_node+0x104/0xab0 mm/slub.c:7279
> > > refill_objects+0x58/0x410 mm/slub.c:7405
> > > refill_sheaf mm/slub.c:2885 [inline]
> > > __pcs_replace_empty_main+0x35e/0x650 mm/slub.c:4774
> > > alloc_from_pcs mm/slub.c:4850 [inline]
> > > slab_alloc_node mm/slub.c:4984 [inline]
> > > __kmalloc_cache_noprof+0x4f4/0x6d0 mm/slub.c:5559
> > > _kmalloc_noprof include/linux/slab.h:991 [inline]
> > > _kzalloc_noprof include/linux/slab.h:1312 [inline]
> > > kvm_async_pf_task_wake arch/x86/kernel/kvm.c:224 [inline]
> > > __sysvec_kvm_asyncpf_interrupt+0x334/0x610 arch/x86/kernel/kvm.c:338
> > > instr_sysvec_kvm_asyncpf_interrupt arch/x86/kernel/kvm.c:327 [inline]
> > > sysvec_kvm_asyncpf_interrupt+0x9e/0xc0 arch/x86/kernel/kvm.c:327
> > > </IRQ>
> > > <TASK>
> > > asm_sysvec_kvm_asyncpf_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:753
> > > RIP: 0010:memcmp+0x156/0x1d0 lib/string.c:665
> > > Code: 0f 86 fb fe ff ff 48 89 d8 48 89 de 48 c1 e8 03 83 e6 07 42 0f b6 14 28 48 8d 43 07 48 89 c1 48 c1 e9 03 40 38 f2 40 0f 9e c6 <84> d2 42 0f b6 0c 29 0f 95 c2 40 84 d6 0f 84 45 ff ff ff be 08 00
> > > RSP: 0018:ffffc90003ab7538 EFLAGS: 00000297
> > > RAX: ffff8880220be413 RBX: ffff8880220be40c RCX: 1ffff11004417c82
> > > RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8880220be40c
> > > RBP: ffffffff8c58a940 R08: 0000000000000001 R09: 0000000000000066
> > > R10: 0000000000000066 R11: 0000000000000001 R12: 0000000000000012
> > > R13: dffffc0000000000 R14: dffffc0000000000 R15: 0000000000000000
> > > strstr+0x109/0x170 lib/string.c:743
> > > tomoyo_add_entry security/tomoyo/common.c:2157 [inline]
> > > tomoyo_supervisor+0xf47/0x1340 security/tomoyo/common.c:2238
> > > tomoyo_audit_path_log security/tomoyo/file.c:169 [inline]
> > > tomoyo_path_permission security/tomoyo/file.c:592 [inline]
> > > tomoyo_path_permission+0x270/0x3b0 security/tomoyo/file.c:577
> > > tomoyo_check_open_permission+0x37f/0x3c0 security/tomoyo/file.c:782
> > > tomoyo_file_open+0x6b/0x90 security/tomoyo/tomoyo.c:334
> > > security_file_open+0xb5/0x1e0 security/security.c:2739
> > > do_dentry_open+0x588/0x14d0 fs/open.c:973
> > > vfs_open+0x82/0x3f0 fs/open.c:1101
> > > do_open fs/namei.c:4836 [inline]
> > > path_openat+0x1a23/0x2450 fs/namei.c:4999
> > > do_file_open+0x20e/0x430 fs/namei.c:5028
> > > do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
> > > do_sys_open fs/open.c:1423 [inline]
> > > __do_sys_openat fs/open.c:1439 [inline]
> > > __se_sys_openat fs/open.c:1434 [inline]
> > > __x64_sys_openat+0x12d/0x210 fs/open.c:1434
> > > do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
> > > do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
> > > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
--
Cheers,
Harry / Hyeonggon
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-10-27 18:48 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2026-10-26 10:19 [syzbot] [kvm?] WARNING: locking bug in __refill_objects_node syzbot
2026-10-26 22:43 ` Hillf Danton
2026-10-27 14:00 ` Sean Christopherson
2026-10-27 18:48 ` Harry Yoo
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