[v6.6] INFO: rcu detected stall in shmem_file_write_iter (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a1153c0deb44 Linux 6.6.147
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17644c9e580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=07015a52da04d299ded0
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9f646bfa1b52/disk-a1153c0d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a2aec2e8f0fd/vmlinux-a1153c0d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a7abe1f87405/bzImage-a1153c0d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+07015a...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P14124/1:b..l P14059/1:b..l
rcu: (detected by 0, t=10502 jiffies, g=92321, q=490 ncpus=1)
task:udevd state:R running task stack:25032 pid:14059 ppid:5140 flags:0x00004002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5382 [inline]
__schedule+0x15ae/0x4660 kernel/sched/core.c:6701
preempt_schedule_common+0x82/0xc0 kernel/sched/core.c:6868
preempt_schedule+0xc0/0xd0 kernel/sched/core.c:6892
preempt_schedule_thunk+0x1a/0x30 arch/x86/entry/thunk_64.S:45
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
_raw_spin_unlock_irqrestore+0x111/0x120 kernel/locking/spinlock.c:194
spin_unlock_irqrestore include/linux/spinlock.h:406 [inline]
__wake_up_common_lock kernel/sched/wait.c:140 [inline]
__wake_up_sync_key+0x12c/0x1a0 kernel/sched/wait.c:213
sock_def_readable+0x1e1/0x420 net/core/sock.c:3363
unix_dgram_sendmsg+0x1093/0x16e0 net/unix/af_unix.c:2143
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
sock_write_iter+0x2dc/0x420 net/socket.c:1161
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x474/0x9a0 fs/read_write.c:584
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f06ddaa7407
RSP: 002b:00007ffd8d8f2010 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f06de24d880 RCX: 00007f06ddaa7407
RDX: 0000000000000000 RSI: 00007ffd8d8f20b7 RDI: 000000000000000a
RBP: 000000000000000a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007f06de24d6e8
R13: 0000000000000000 R14: 0000000000000000 R15: 00005573749c3690
</TASK>
task:syz.1.2657 state:R running task stack:26408 pid:14124 ppid:13252 flags:0x00004002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5382 [inline]
__schedule+0x15ae/0x4660 kernel/sched/core.c:6701
preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7011
irqentry_exit+0x67/0x70 kernel/entry/common.c:438
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:rcu_read_lock include/linux/rcupdate.h:787 [inline]
RIP: 0010:page_ext_get+0x4b/0x2b0 mm/page_ext.c:508
Code: 00 48 c7 c7 a0 1d 13 8d 31 f6 31 d2 b9 02 00 00 00 45 31 c0 45 31 c9 53 e8 b2 aa 7d ff 48 83 c4 08 e8 19 f1 a1 08 89 c5 31 ff <89> c6 e8 5e 98 9c ff 85 ed 74 10 e8 f5 5e 86 ff 84 c0 74 0e e8 9c
RSP: 0018:ffffc900042572b8 EFLAGS: 00000246
RAX: 0000000000000001 RBX: ffffffff81eada42 RCX: ffff888021641e00
RDX: 0000000000000000 RSI: ffffffff8acadd60 RDI: 0000000000000000
RBP: 0000000000000001 R08: dffffc0000000000 R09: 1ffffffff223d6a0
R10: dffffc0000000000 R11: fffffbfff223d6a1 R12: 00fff00000000000
R13: dffffc0000000000 R14: ffffea000143e380 R15: ffffea000143e380
__page_table_check_zero+0x138/0x4b0 mm/page_table_check.c:148
prep_new_page mm/page_alloc.c:1589 [inline]
get_page_from_freelist+0x2181/0x22a0 mm/page_alloc.c:3221
__alloc_pages+0x1f0/0x460 mm/page_alloc.c:4501
__folio_alloc+0x10/0x20 mm/page_alloc.c:4533
vma_alloc_folio+0x474/0x8f0 mm/mempolicy.c:2240
shmem_alloc_folio+0x1a9/0x2a0 mm/shmem.c:1679
shmem_alloc_and_acct_folio+0x1cb/0x6c0 mm/shmem.c:1704
shmem_get_folio_gfp+0xe1d/0x2b40 mm/shmem.c:2041
shmem_get_folio mm/shmem.c:2164 [inline]
shmem_write_begin+0xf2/0x430 mm/shmem.c:2706
generic_perform_write+0x2fe/0x5c0 mm/filemap.c:4036
shmem_file_write_iter+0xfb/0x120 mm/shmem.c:2883
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x474/0x9a0 fs/read_write.c:584
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fd5e7d5e84e
RSP: 002b:00007fd5e8d08da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fd5e8d096c0 RCX: 00007fd5e7d5e84e
RDX: 0000000004000000 RSI: 00007fd5ddbf7000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007fd5e8d08ee0 R14: 00007fd5e8d08ea0 R15: 00007fd5ddbf7000
</TASK>
rcu: rcu_preempt kthread starved for 10502 jiffies! g92321 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
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:27848 pid:17 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5382 [inline]
__schedule+0x15ae/0x4660 kernel/sched/core.c:6701
schedule+0xbd/0x170 kernel/sched/core.c:6775
schedule_timeout+0x188/0x2d0 kernel/time/timer.c:2168
rcu_gp_fqs_loop+0x30d/0x1590 kernel/rcu/tree.c:1667
rcu_gp_kthread+0x9d/0x3b0 kernel/rcu/tree.c:1866
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 PID: 14153 Comm: syz.4.2666 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:check_kcov_mode kernel/kcov.c:184 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x30/0x60 kernel/kcov.c:216
Code: 04 24 65 48 8b 0d 10 49 7c 7e 65 8b 15 11 49 7c 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 35 83 b9 1c 16 00 00 00 74 2c <8b> 91 f8 15 00 00 83 fa 02 75 21 48 8b 91 00 16 00 00 48 8b 32 48
RSP: 0018:ffffc9000449faa0 EFLAGS: 00000246
RAX: ffffffff813256c7 RBX: ffffc9000449fb60 RCX: ffff888026659e00
RDX: 0000000000000000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: 0000000000000000 R08: ffffffff8e8c7caf R09: 1ffffffff1d18f95
R10: dffffc0000000000 R11: fffffbfff1d18f96 R12: 0000000000000340
R13: dffffc0000000000 R14: 00007fbf41af1fa8 R15: ffffc9000449fb80
FS: 00007fbf41af26c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbf40beb700 CR3: 00000000684a0000 CR4: 00000000003506f0
DR0: ffffffffffffffff DR1: 00000000000001f8 DR2: 0000000000000083
DR3: ffffffffefffff15 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
_static_cpu_has arch/x86/include/asm/cpufeature.h:175 [inline]
use_xsave arch/x86/kernel/fpu/internal.h:10 [inline]
xstate_sigframe_size arch/x86/kernel/fpu/signal.c:451 [inline]
fpu__alloc_mathframe+0x77/0x120 arch/x86/kernel/fpu/signal.c:506
get_sigframe+0x4c3/0x7d0 arch/x86/kernel/signal.c:113
x64_setup_rt_frame+0x164/0xc30 arch/x86/kernel/signal_64.c:175
setup_rt_frame arch/x86/kernel/signal.c:223 [inline]
handle_signal arch/x86/kernel/signal.c:267 [inline]
arch_do_signal_or_restart+0x411/0x7b0 arch/x86/kernel/signal.c:312
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fbf40b9e017
Code: 83 c8 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
RSP: 002b:00007fbf41af2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000048
RAX: 0000000000000048 RBX: 00007fbf40e25fa0 RCX: 00007fbf40b9e019
RDX: 0000200000000280 RSI: 0000000000000026 RDI: 0000000000000003
RBP: 00007fbf40c3500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbf40e26038 R14: 00007fbf40e25fa0 R15: 00007ffd47c20d88
</TASK>
sched: RT throttling activated


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