syzbot
INFO: rcu detected stall in sys_readlink (5)
Status:
upstream: reported on 2026/08/24 16:16
Reported-by: syzbot+0b6c27dc2b15b79b43f7@syzkaller.appspotmail.com
First crash: 3d11h, last: 3d11h
Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P4505/1:b..l P4495/1:b..l P3557/1:b..l
(detected by 0, t=10503 jiffies, g=8225, q=399)
task:udevd state:R running task stack:25584 pid: 3557 ppid: 1 flags:0x00004002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11c3/0x4350 kernel/sched/core.c:6395
preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6799
irqentry_exit+0x63/0x70 kernel/entry/common.c:432
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:seqcount_lockdep_reader_access+0x195/0x1d0 include/linux/seqlock.h:106
Code: ff 4d 85 ed 75 16 e8 aa 61 ac ff eb 15 e8 a3 61 ac ff e8 2e a6 f3 07 4d 85 ed 74 ea e8 94 61 ac ff fb 48 c7 04 24 0e 36 e0 45 <4b> c7 04 27 00 00 00 00 43 c7 44 27 08 00 00 00 00 65 48 8b 04 25
RSP: 0018:ffffc90002ddf8c0 EFLAGS: 00000293
RAX: ffffffff81cc9e0c RBX: 0000000000000000 RCX: ffff88807cc31dc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90002ddf970 R08: ffffffff8d8b0d6f R09: 1ffffffff1b161ad
R10: dffffc0000000000 R11: fffffbfff1b161ae R12: dffffc0000000000
R13: 0000000000000200 R14: ffffffff81ccac57 R15: 1ffff920005bbf18
__follow_mount_rcu fs/namei.c:1465 [inline]
handle_mounts fs/namei.c:1498 [inline]
step_into+0x627/0xcd0 fs/namei.c:1814
link_path_walk+0x688/0xde0 fs/namei.c:-1
path_lookupat+0x83/0x420 fs/namei.c:2462
filename_lookup+0x21e/0x550 fs/namei.c:2492
user_path_at_empty+0x40/0x190 fs/namei.c:2934
do_readlinkat+0xd9/0x490 fs/stat.c:442
__do_sys_readlink fs/stat.c:475 [inline]
__se_sys_readlink fs/stat.c:472 [inline]
__x64_sys_readlink+0x7b/0x90 fs/stat.c:472
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7ff35caeb3a7
RSP: 002b:00007ffccc4f5558 EFLAGS: 00000246 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffccc4f5a30 RCX: 00007ff35caeb3a7
RDX: 0000000000000400 RSI: 00007ffccc4f5560 RDI: 00007ffccc4f5a30
RBP: 00007ffccc4f5560 R08: 000055e898eacd04 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000400
R13: 00000000000000fe R14: 000055e897703be0 R15: 00007ffccc4f6540
</TASK>
task:modprobe state:R running task stack:27696 pid: 4495 ppid: 4346 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11c3/0x4350 kernel/sched/core.c:6395
preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6799
irqentry_exit+0x63/0x70 kernel/entry/common.c:432
asm_sysvec_reschedule_ipi+0x16/0x20 arch/x86/include/asm/idtentry.h:681
RIP: 0010:lock_acquire+0x208/0x400 kernel/locking/lockdep.c:5627
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3d 04 f8 0f 85 f1 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 43 c7 44 3d 08 00 00 00 00 65 48 8b 04
RSP: 0018:ffffc900034b77a0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 3d970297ecd91300
RDX: 0000000000000000 RSI: ffffffff8a2b3e80 RDI: ffffffff8a7a42c0
RBP: ffffc900034b78c0 R08: dffffc0000000000 R09: 1ffffffff203de18
R10: dffffc0000000000 R11: fffffbfff203de19 R12: ffffffff8c31ef60
R13: 1ffff92000696f00 R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:313
rcu_read_lock include/linux/rcupdate.h:740 [inline]
filemap_get_read_batch+0xd6/0x760 mm/filemap.c:2340
filemap_get_pages mm/filemap.c:2547 [inline]
filemap_read+0x537/0x2560 mm/filemap.c:2634
call_read_iter include/linux/fs.h:2173 [inline]
new_sync_read fs/read_write.c:404 [inline]
vfs_read+0x75e/0xd50 fs/read_write.c:485
ksys_pread64 fs/read_write.c:675 [inline]
__do_sys_pread64 fs/read_write.c:685 [inline]
__se_sys_pread64 fs/read_write.c:682 [inline]
__x64_sys_pread64+0x197/0x220 fs/read_write.c:682
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f8d4918c10a
RSP: 002b:00007ffe803becc8 EFLAGS: 00000202 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 0000000000000310 RCX: 00007f8d4918c10a
RDX: 0000000000000310 RSI: 00007ffe803becd0 RDI: 0000000000000000
RBP: 00007ffe803bf140 R08: 000000000000c0ff R09: 0000000000000000
R10: 0000000000000040 R11: 0000000000000202 R12: 0000000000000003
R13: 00007f8d491685f0 R14: 00007ffe803bf1e0 R15: 0000000000000000
</TASK>
task:modprobe state:R running task stack:27696 pid: 4505 ppid: 307 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11c3/0x4350 kernel/sched/core.c:6395
preempt_schedule_notrace+0xd9/0x120 kernel/sched/core.c:6650
preempt_schedule_notrace_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:35
rcu_lockdep_current_cpu_online+0x10b/0x130 kernel/rcu/tree.c:1175
rcu_read_lock_held_common kernel/rcu/update.c:112 [inline]
rcu_read_lock_held+0x1a/0x40 kernel/rcu/update.c:309
count_memcg_event_mm+0x13b/0x370 include/linux/memcontrol.h:1079
handle_mm_fault+0x134/0x4440 mm/memory.c:4863
do_user_addr_fault+0x494/0xc90 arch/x86/mm/fault.c:1355
handle_page_fault arch/x86/mm/fault.c:1443 [inline]
exc_page_fault+0x60/0x100 arch/x86/mm/fault.c:1496
asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:606
RIP: 0033:0x7fc040b2bff2
RSP: 002b:00007ffe237390d8 EFLAGS: 00010206
RAX: 00007fc040839068 RBX: 0000000000000004 RCX: 00007fc04083b6d0
RDX: 0000000000000f98 RSI: 0000000000000000 RDI: 00007fc040839068
RBP: 00007ffe237394a0 R08: 00007fc040839068 R09: 0000000000000003
R10: 0000000000000812 R11: 00007ffe23739588 R12: 00007ffe23739188
R13: 00007fc040b08ab0 R14: 00007ffe23739540 R15: 00007fc04083a000
</TASK>
rcu: rcu_preempt kthread starved for 10473 jiffies! g8225 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt state:R running task stack:28112 pid: 15 ppid: 2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11c3/0x4350 kernel/sched/core.c:6395
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
rcu_gp_fqs_loop+0x2be/0x11f0 kernel/rcu/tree.c:1972
rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4475 Comm: syz.4.45 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:arch_irqs_disabled_flags arch/x86/include/asm/irqflags.h:127 [inline]
RIP: 0010:lock_acquire+0x16d/0x400 kernel/locking/lockdep.c:5624
Code: 9c 8f 84 24 a0 00 00 00 4c 8b b4 24 a0 00 00 00 43 c6 44 3d 08 f8 fa 48 c7 c7 e0 39 2b 8a e8 4a 79 63 08 65 ff 05 33 9d a5 7e <45> 31 c9 41 f7 c6 00 02 00 00 41 0f 94 c1 4c 89 e7 8b 74 24 1c 89
RSP: 0000:ffffc9000329fdc0 EFLAGS: 00000002
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 246bc86627455100
RDX: 0000000000000000 RSI: ffffffff8a2b39e0 RDI: ffffffff8a7a42c0
RBP: ffffc9000329fec8 R08: ffffffff8d8b0d6f R09: 1ffffffff1b161ad
R10: dffffc0000000000 R11: fffffbfff1b161ae R12: ffff888028490728
R13: 1ffff92000653fc4 R14: 0000000000000046 R15: dffffc0000000000
FS: 00007f948bb8c6c0(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000bbdffc CR3: 0000000023413000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
do_write_seqcount_begin_nested include/linux/seqlock.h:519 [inline]
do_write_seqcount_begin include/linux/seqlock.h:545 [inline]
vtime_user_enter+0x96/0x2c0 kernel/sched/cputime.c:702
__context_tracking_enter+0x60/0x90 kernel/context_tracking.c:82
user_enter_irqoff include/linux/context_tracking.h:41 [inline]
__exit_to_user_mode kernel/entry/common.c:136 [inline]
irqentry_exit_to_user_mode+0x29/0x30 kernel/entry/common.c:322
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0033:0x7f948d974650
Code: 83 c0 16 83 e0 f7 74 12 50 48 8d 3d ca 2c 07 00 e8 65 65 f9 ff 0f 1f 44 00 00 c3 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 <83> ff 21 74 0b c3 66 2e 0f 1f 84 00 00 00 00 00 55 53 48 89 f3 48
RSP: 002b:00007f948bb8ba78 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 00007f948dbdd090 RCX: 00007f948d9550d9
RDX: 00007f948bb8ba80 RSI: 00007f948bb8bbb0 RDI: 0000000000000021
RBP: 00007f948d9ec024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000020000023896 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f948dbdd128 R14: 00007f948dbdd090 R15: 00007ffdaeb915a8
</TASK>
Struck through repros no longer work on HEAD.