INFO: rcu detected stall in shmem_fault (2)

Status: upstream: reported on 2026/10/05 16:19
Reported-by: syzbot+fdeff3b0ca6f812bbafa@syzkaller.appspotmail.com
First crash: 15h56m, last: 15h56m
▶ ▼ Similar bugs (12)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in shmem_fault (4) kernel 1 1 1375d 1375d 0/29 auto-obsoleted due to no activity on 2023/04/08 07:17
linux-5.15 INFO: rcu detected stall in shmem_fault (2) 1 29 20d 854d 0/3 upstream: reported on 2024/06/03 20:13
upstream INFO: rcu detected stall in shmem_fault mm 1 13 2758d 2918d 0/29 closed as dup on 2019/01/02 16:58
linux-6.6 INFO: rcu detected stall in shmem_fault 1 9 223d 476d 0/2 auto-obsoleted due to no activity on 2026/06/04 20:40
linux-6.1 INFO: rcu detected stall in shmem_fault 1 7 786d 850d 0/3 auto-obsoleted due to no activity on 2024/11/18 20:23
upstream INFO: rcu detected stall in shmem_fault (5) cgroups mm 1 3 1145d 1165d 23/29 fixed on 2023/10/12 12:48
linux-5.15 INFO: rcu detected stall in shmem_fault 1 1 1129d 1129d 0/3 auto-obsoleted due to no activity on 2023/12/11 11:17
upstream INFO: rcu detected stall in shmem_fault (3) mm fs 1 4 1624d 1624d 0/29 auto-closed as invalid on 2022/06/25 08:10
linux-6.1 INFO: rcu detected stall in shmem_fault (2) 1 22 142d 657d 0/3 auto-obsoleted due to no activity on 2026/08/25 07:39
upstream INFO: rcu detected stall in shmem_fault (2) cgroups mm 1 1 2497d 2497d 0/29 closed as invalid on 2019/12/04 14:04
upstream INFO: rcu detected stall in shmem_fault (6) mm prio:low 1 syz, C 275 1d19h 746d 0/29 upstream: reported C repro on 2024/09/19 14:28
upstream BUG: workqueue lockup (5) prio:low kernel 1 syz, C done 17896 24m 2456d 0/29 upstream: reported C repro on 2020/01/14 22:04

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P16621/1:b..l P16700/1:b..l P16182/1:b..l
rcu: 	(detected by 1, t=10502 jiffies, g=77253, q=319 ncpus=2)
task:syz.0.3039      state:R  running task     stack:19880 pid:16182 ppid:5775   flags:0x00104006
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:441
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:check_region_inline mm/kasan/generic.c:-1 [inline]
RIP: 0010:kasan_check_range+0x18/0x290 mm/kasan/generic.c:187
Code: ff c3 0f 0b b8 ea ff ff ff c3 cc cc cc cc cc cc cc cc 66 0f 1f 00 b0 01 48 85 f6 0f 84 b4 01 00 00 55 41 57 41 56 41 55 41 54 <53> 4c 8d 04 37 49 39 f8 0f 82 13 02 00 00 49 89 f9 49 c1 e9 2f 41
RSP: 0018:ffffc90010386610 EFLAGS: 00000202
RAX: 0000000000000001 RBX: dffffc0000000000 RCX: ffffffff81e9840c
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff88801a08a648
RBP: 000000000000000a R08: dffffc0000000000 R09: 1ffffffff223e0a0
R10: dffffc0000000000 R11: fffffbfff223e0a1 R12: ffff88801ab244b8
R13: 000000000000000b R14: ffff88801a08a670 R15: ffff88801a08a648
 instrument_write include/linux/instrumented.h:40 [inline]
 ___set_bit include/asm-generic/bitops/instrumented-non-atomic.h:28 [inline]
 __set_page_owner_handle+0x23c/0x3c0 mm/page_owner.c:179
 __set_page_owner+0x45/0x60 mm/page_owner.c:197
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1582
 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_fault+0x1b8/0x820 mm/shmem.c:2248
 __do_fault+0x13b/0x4d0 mm/memory.c:4244
 do_read_fault mm/memory.c:4638 [inline]
 do_fault mm/memory.c:4775 [inline]
 do_pte_missing mm/memory.c:3689 [inline]
 handle_pte_fault mm/memory.c:5047 [inline]
 __handle_mm_fault mm/memory.c:5188 [inline]
 handle_mm_fault+0x3945/0x4a50 mm/memory.c:5353
 faultin_page mm/gup.c:868 [inline]
 __get_user_pages+0x604/0x1580 mm/gup.c:1167
 __get_user_pages_locked mm/gup.c:1431 [inline]
 get_dump_page+0x10c/0x200 mm/gup.c:1939
 dump_user_range+0x127/0x840 fs/coredump.c:983
 elf_core_dump+0x320e/0x37c0 fs/binfmt_elf.c:2184
 do_coredump+0x1791/0x24a0 fs/coredump.c:834
 get_signal+0x10da/0x1390 kernel/signal.c:2901
 arch_do_signal_or_restart+0xc2/0x7b0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:177
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:213
 irqentry_exit_to_user_mode+0x9/0x30 kernel/entry/common.c:318
 exc_page_fault+0x8c/0x100 arch/x86/mm/fault.c:1519
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:608
RIP: 0033:0x7f8f21853bd7
RSP: 002b:00007f8f22833120 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 000000000000000b RCX: 00007f8f2199e199
RDX: 00007f8f22833140 RSI: 00007f8f22833270 RDI: 000000000000000b
RBP: 00007f8f21a350b8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f8f21c26128 R14: 00007f8f21c26090 R15: 00007fffa492c038
 </TASK>
task:syz.3.3173      state:R  running task     stack:26568 pid:16700 ppid:5777   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:441
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:debug_lockdep_rcu_enabled+0x0/0x30 kernel/rcu/update.c:318
Code: 83 3d d3 e5 f9 03 00 75 d8 48 c7 c7 80 cb ca 8a 48 c7 c6 a0 ef ca 8a e8 de 9d be f6 0f 0b eb c1 cc cc cc cc cc cc cc cc cc cc <f3> 0f 1e fa 31 c0 83 3d 1f b2 f9 03 00 74 1d 83 3d 96 e5 f9 03 00
RSP: 0018:ffffc90003497778 EFLAGS: 00000287
RAX: ffffffff81cb1d1c RBX: 1ffff92000692ef4 RCX: 0000000000080000
RDX: ffffc9000e3af000 RSI: 0000000000038681 RDI: 0000000000038682
RBP: ffffc90003497850 R08: ffffffff911f0537 R09: 1ffffffff223e0a6
R10: dffffc0000000000 R11: fffffbfff223e0a7 R12: 0000000000000200
R13: dffffc0000000000 R14: 0000000000000000 R15: ffffffff81cb1ace
 rcu_read_unlock include/linux/rcupdate.h:815 [inline]
 count_memcg_event_mm+0x2e2/0x3c0 include/linux/memcontrol.h:1104
 mm_account_fault mm/memory.c:5222 [inline]
 handle_mm_fault+0x28c0/0x4a50 mm/memory.c:5369
 do_user_addr_fault+0x736/0x12d0 arch/x86/mm/fault.c:1371
 handle_page_fault arch/x86/mm/fault.c:1463 [inline]
 exc_page_fault+0x64/0x100 arch/x86/mm/fault.c:1516
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:608
RIP: 0010:rep_movs_alternative+0x4a/0x90 arch/x86/lib/copy_user_64.S:71
Code: 75 f1 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 8b 06 48 89 07 48 83 c6 08 48 83 c7 08 83 e9 08 74 df 83 f9 08 73 e8 eb c9 <f3> a4 c3 48 8b 06 48 89 07 48 8d 47 08 48 83 e0 f8 48 29 f8 48 01
RSP: 0018:ffffc90003497bd0 EFLAGS: 00050206
RAX: ffffffff84348a01 RBX: 00000000000e0043 RCX: 000000000003e358
RDX: 0000000000000001 RSI: 00002000006c2000 RDI: ffff88803d5a1ceb
RBP: ffffc90003497d20 R08: 0000000000000002 R09: 0000000000000003
R10: dffffc0000000000 R11: ffffed1007abc008 R12: 0000200000700358
R13: 1ffff92000692fbd R14: ffff88803d500000 R15: 0000200000620315
 copy_user_generic arch/x86/include/asm/uaccess_64.h:112 [inline]
 raw_copy_from_user arch/x86/include/asm/uaccess_64.h:127 [inline]
 _copy_from_user+0x8b/0xe0 lib/usercopy.c:23
 copy_from_user include/linux/uaccess.h:183 [inline]
 generic_map_update_batch+0x58c/0x800 kernel/bpf/syscall.c:1797
 bpf_map_do_batch+0x3f2/0x600 kernel/bpf/syscall.c:5024
 __sys_bpf+0x381/0x890 kernel/bpf/syscall.c:-1
 __do_sys_bpf kernel/bpf/syscall.c:5598 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5596 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5596
 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: 0033:0x7fc50999e199
RSP: 002b:00007fc50a92b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007fc509c26090 RCX: 00007fc50999e199
RDX: 0000000000000038 RSI: 0000200000000240 RDI: 000000000000001a
RBP: 00007fc509a350b8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc509c26128 R14: 00007fc509c26090 R15: 00007ffe5fe0a788
 </TASK>
task:syz.0.3144      state:R  running task     stack:19624 pid:16621 ppid:5775   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:441
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:lock_acquire+0x208/0x420 kernel/locking/lockdep.c:5794
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3c 04 f8 0f 85 f0 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 43 c7 44 3c 08 00 00 00 00 65 48 8b 04 25
RSP: 0018:ffffc900032c6d20 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 433359f2d8110000
RDX: 0000000000000000 RSI: ffffffff8acade60 RDI: ffffffff8b1d4020
RBP: ffffc900032c6e38 R08: dffffc0000000000 R09: 1ffffffff223e0a0
R10: dffffc0000000000 R11: fffffbfff223e0a1 R12: 1ffff92000658db0
R13: ffffffff8d1320e0 R14: 0000000000000246 R15: dffffc0000000000
 rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 rcu_read_lock include/linux/rcupdate.h:786 [inline]
 blk_cgroup_congested+0x3b/0x220 block/blk-cgroup.c:2206
 __folio_throttle_swaprate+0x71/0x1a0 mm/swapfile.c:3656
 folio_throttle_swaprate include/linux/swap.h:649 [inline]
 shmem_add_to_page_cache+0x9a0/0x1b80 mm/shmem.c:793
 shmem_get_folio_gfp+0x1037/0x2b40 mm/shmem.c:2071
 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
 __kernel_write_iter+0x29f/0x6d0 fs/read_write.c:517
 dump_emit_page fs/coredump.c:958 [inline]
 dump_user_range+0x418/0x840 fs/coredump.c:985
 elf_core_dump+0x320e/0x37c0 fs/binfmt_elf.c:2184
 do_coredump+0x1791/0x24a0 fs/coredump.c:834
 get_signal+0x10da/0x1390 kernel/signal.c:2901
 arch_do_signal_or_restart+0xc2/0x7b0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:177
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:213
 irqentry_exit_to_user_mode+0x9/0x30 kernel/entry/common.c:318
 exc_page_fault+0x8c/0x100 arch/x86/mm/fault.c:1519
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:608
RIP: 0033:0x7f8f2199e1a1
RSP: 002b:fffffffffffffe70 EFLAGS: 00010217
RAX: 0000000000000000 RBX: 00007f8f21c26090 RCX: 00007f8f2199e199
RDX: 0000000000000000 RSI: fffffffffffffe70 RDI: 0000000000008000
RBP: 00007f8f21a350b8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f8f21c26128 R14: 00007f8f21c26090 R15: 00007fffa492c038
 </TASK>
rcu: rcu_preempt kthread starved for 10647 jiffies! g77253 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:26856 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:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
RIP: 0010:pv_native_safe_halt+0xf/0x10 arch/x86/kernel/paravirt.c:148
Code: 69 17 02 c3 cc cc cc cc cc cc cc f3 0f 1e fa 0f 0b 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 66 90 0f 00 2d 13 96 35 00 fb f4 <c3> 66 0f 1f 00 55 41 57 41 56 41 54 53 50 8b 2f eb 2c 89 cb 80 f9
RSP: 0018:ffffffff8ce07d80 EFLAGS: 000002c6
RAX: 6a3da4cf08d21a00 RBX: ffffffff81631e31 RCX: 6a3da4cf08d21a00
RDX: 0000000000000001 RSI: ffffffff8acacce0 RDI: ffffffff8b1d4020
RBP: ffffffff8ce07eb8 R08: ffff8880b8e36b6b R09: 1ffff110171c6d6d
R10: dffffc0000000000 R11: ffffed10171c6d6e R12: 1ffffffff19c0fbc
R13: dffffc0000000000 R14: 1ffffffff19d2688 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7d99600218 CR3: 00000000785f3000 CR4: 00000000003506f0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:108 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:753
 default_idle_call+0x6c/0xa0 kernel/sched/idle.c:97
 cpuidle_idle_call kernel/sched/idle.c:178 [inline]
 do_idle+0x221/0x5c0 kernel/sched/idle.c:302
 cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:401
 rest_init+0x2e2/0x300 init/main.c:705
 arch_call_rest_init+0xe/0x10 init/main.c:801
 start_kernel+0x461/0x4e0 init/main.c:1046
 x86_64_start_reservations+0x2a/0x30 arch/x86/kernel/head64.c:555
 x86_64_start_kernel+0x60/0x60 arch/x86/kernel/head64.c:536
 secondary_startup_64_no_verify+0x179/0x17b
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/05 16:19 linux-6.6.y a91a6aa9253c af63e995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in shmem_fault
* Struck through repros no longer work on HEAD.