possible deadlock in refcount_dec_and_mutex_lock (2)

Status: auto-obsoleted due to no activity on 2026/10/23 09:15
Subsystems: perf
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+196a82fd904572696b3c@syzkaller.appspotmail.com
First crash: 253d, last: 193d
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
4804df34 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in refcount_dec_and_mutex_lock (2) 2026/05/16 20:25 2026/05/16 20:25 2026/05/16 20:56 de5aae85
▶ ▼ Discussions (3)
Title Replies (including bot) Last reply
[syzbot] Monthly perf report (May 2026) 0 (1) 2026/05/19 04:32
[PATCH] perf: Fix deadlock in perf_mmap() 15 (15) 2026/03/27 12:34
[syzbot] [perf?] possible deadlock in refcount_dec_and_mutex_lock (2) 3 (6) 2026/03/09 06:40
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in refcount_dec_and_mutex_lock nbd 4 1 2611d 2607d 0/29 auto-closed as invalid on 2019/11/20 04:39
linux-4.19 possible deadlock in refcount_dec_and_mutex_lock 4 syz, C done done 5 2512d 2568d 1/1 fixed on 2020/01/28 16:29
linux-4.14 possible deadlock in refcount_dec_and_mutex_lock 4 syz, C done 10 2515d 2588d 1/1 fixed on 2020/01/25 22:00
▶ ▼ Last patch testing requests (10)
Created Duration User Patch Repo Result
2026/10/23 08:52 22m retest repro upstream no crash job log log
2026/10/23 07:34 23m retest repro upstream no crash job log log
2026/08/14 07:41 16m retest repro upstream error job log
2026/08/14 05:49 14m retest repro upstream error job log
2026/06/05 06:14 22m retest repro upstream error
2026/06/05 05:23 21m retest repro upstream error
2026/03/27 05:04 18m retest repro upstream error
2026/03/27 05:04 17m retest repro upstream error
2026/03/09 06:22 17m wangqing7171@gmail.com patch upstream error
2026/03/09 05:57 19m wangqing7171@gmail.com patch upstream error

Sample crash report:
FAULT_INJECTION: forcing a failure.
name fail_page_alloc, interval 1, probability 0, space 0, times 1
CPU: 0 UID: 0 PID: 5320 Comm: syz.0.0 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_lvl+0xe8/0x150 lib/dump_stack.c:120
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x412/0x560 lib/fault-inject.c:174
 prepare_alloc_pages+0x22a/0x650 mm/page_alloc.c:5002
 __alloc_frozen_pages_noprof+0x12f/0x380 mm/page_alloc.c:5215
 alloc_pages_mpol+0x235/0x490 mm/mempolicy.c:2490
 alloc_frozen_pages_noprof mm/mempolicy.c:2561 [inline]
 alloc_pages_noprof+0xac/0x2a0 mm/mempolicy.c:2581
 pagetable_alloc_noprof include/linux/mm.h:3651 [inline]
 __pte_alloc_one_noprof include/asm-generic/pgalloc.h:76 [inline]
 pte_alloc_one+0x22/0x370 arch/x86/mm/pgtable.c:18
 __pte_alloc+0x25/0x1a0 mm/memory.c:453
 remap_pte_range mm/memory.c:2903 [inline]
 remap_pmd_range mm/memory.c:2936 [inline]
 remap_pud_range mm/memory.c:2958 [inline]
 remap_p4d_range mm/memory.c:2980 [inline]
 remap_pfn_range_internal mm/memory.c:3027 [inline]
 remap_pfn_range_notrack mm/memory.c:3043 [inline]
 remap_pfn_range_track mm/memory.c:3113 [inline]
 do_remap_pfn_range+0xbe6/0x1250 mm/memory.c:3126
 map_range+0x199/0x230 kernel/events/core.c:7206
 perf_mmap+0x3ff/0x490 kernel/events/core.c:7482
 vfs_mmap include/linux/fs.h:2071 [inline]
 mmap_file mm/internal.h:168 [inline]
 __mmap_new_file_vma mm/vma.c:2496 [inline]
 __mmap_new_vma mm/vma.c:2562 [inline]
 __mmap_region mm/vma.c:2771 [inline]
 mmap_region+0x19a3/0x22a0 mm/vma.c:2857
 do_mmap+0xc39/0x10c0 mm/mmap.c:560
 vm_mmap_pgoff+0x2c9/0x4f0 mm/util.c:581
 ksys_mmap_pgoff+0x51e/0x760 mm/mmap.c:606
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0001b9cdd9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f000296efe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f0001e16090 RCX: 00007f0001b9cdd9
RDX: 0000000001000008 RSI: 0000000000002000 RDI: 0000200000ffe000
RBP: 00007f000296f050 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000000013 R11: 0000000000000246 R12: 0000000000000002
R13: 00007f0001e16128 R14: 00007f0001e16090 R15: 00007ffe67baaeb8
 </TASK>
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.0/5320 is trying to acquire lock:
ffff88801fce09c0 (&event->mmap_mutex){+.+.}-{4:4}, at: refcount_dec_and_mutex_lock+0x30/0xa0 lib/refcount.c:118

but task is already holding lock:
ffff88801fce09c0 (&event->mmap_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
ffff88801fce09c0 (&event->mmap_mutex){+.+.}-{4:4}, at: perf_mmap+0x1bb/0x490 kernel/events/core.c:7449

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

       CPU0
       ----
  lock(&event->mmap_mutex);
  lock(&event->mmap_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz.0.0/5320:
 #0: ffff8880129958f8 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
 #0: ffff8880129958f8 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x234/0x4f0 mm/util.c:579
 #1: ffff88801fce09c0 (&event->mmap_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
 #1: ffff88801fce09c0 (&event->mmap_mutex){+.+.}-{4:4}, at: perf_mmap+0x1bb/0x490 kernel/events/core.c:7449

stack backtrace:
CPU: 0 UID: 0 PID: 5320 Comm: syz.0.0 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_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x253f/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a3/0x1550 kernel/locking/mutex.c:820
 refcount_dec_and_mutex_lock+0x30/0xa0 lib/refcount.c:118
 perf_mmap_close+0x953/0xf90 kernel/events/core.c:7060
 perf_mmap+0x41b/0x490 kernel/events/core.c:7484
 vfs_mmap include/linux/fs.h:2071 [inline]
 mmap_file mm/internal.h:168 [inline]
 __mmap_new_file_vma mm/vma.c:2496 [inline]
 __mmap_new_vma mm/vma.c:2562 [inline]
 __mmap_region mm/vma.c:2771 [inline]
 mmap_region+0x19a3/0x22a0 mm/vma.c:2857
 do_mmap+0xc39/0x10c0 mm/mmap.c:560
 vm_mmap_pgoff+0x2c9/0x4f0 mm/util.c:581
 ksys_mmap_pgoff+0x51e/0x760 mm/mmap.c:606
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0001b9cdd9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f000296efe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f0001e16090 RCX: 00007f0001b9cdd9
RDX: 0000000001000008 RSI: 0000000000002000 RDI: 0000200000ffe000
RBP: 00007f000296f050 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000000013 R11: 0000000000000246 R12: 0000000000000002
R13: 00007f0001e16128 R14: 00007f0001e16090 R15: 00007ffe67baaeb8
 </TASK>

Crashes (11):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/05 23:25 upstream 9207d47f966b 26da2c66 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/05/05 23:10 upstream 9207d47f966b 26da2c66 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/04/17 20:35 upstream 43cfbdda5af6 24ecfc1e .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/04/14 19:17 upstream d60bc1401583 362d1323 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/04/09 04:28 upstream 7f87a5ea75f0 38c8e246 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/04/01 06:31 upstream dbf00d8d23b4 fb8b2c26 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/03/13 04:37 upstream 8004279c41ad 2f7f359d .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/03/08 14:16 upstream c23719abc330 5cb44a80 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/03/06 18:41 upstream 5ee8dbf54602 41d8037d .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/03/06 18:11 upstream 5ee8dbf54602 41d8037d .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
2026/03/06 17:43 upstream 5ee8dbf54602 41d8037d .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root possible deadlock in refcount_dec_and_mutex_lock
* Struck through repros no longer work on HEAD.