[syzbot] [mm?] [kasan?] INFO: rcu detected stall in filemap_read

[syzbot <syzbot+eead920cc4166b2530d8@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    4235cb24ec1e Merge tag 'vfs-7.2-rc5.fixes' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12e3bfde580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4e38b15c29e6a1d9
dashboard link: https://syzkaller.appspot.com/bug?extid=eead920cc4166b2530d8
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10dde6b9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/906b09e16f16/disk-4235cb24.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2cb120bc3818/vmlinux-4235cb24.xz
kernel image: https://storage.googleapis.com/syzbot-assets/880615d1b5d5/bzImage-4235cb24.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+eead920cc4166b2530d8@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	1-...!: (3 ticks this GP) idle=ff84/1/0x4000000000000000 softirq=18226/18246 fqs=4
rcu: 	(detected by 0, t=10502 jiffies, g=18401, q=1937 ncpus=2)
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 6111 Comm: modprobe Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:__kasan_check_byte+0x14/0x40 mm/kasan/common.c:573
Code: fa ff ff 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 41 56 53 48 89 f3 49 89 fe e8 3e 15 00 00 84 c0 <75> 16 be 01 00 00 00 4c 89 f7 31 d2 48 89 d9 89 c3 e8 f6 04 00 00
RSP: 0018:ffffc90000a08c58 EFLAGS: 00000002
RAX: 0000000000000001 RBX: ffffffff89de25b4 RCX: 0000000000010001
RDX: 0000000000000000 RSI: ffffffff89de25b4 RDI: 1ffffffff1d6b38c
RBP: ffffffff89de2598 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed100f925c56 R12: 0000000000000002
R13: ffffffff8eb59c60 R14: ffffffff8eb59c60 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff88812504e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa1a832efe8 CR3: 000000002d63f000 CR4: 0000000000350ef0
Call Trace:
 <IRQ>
 kasan_check_byte include/linux/kasan.h:402 [inline]
 lock_acquire+0x84/0x350 kernel/locking/lockdep.c:5842
 rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 rcu_read_lock include/linux/rcupdate.h:840 [inline]
 advance_sched+0xa04/0xc80 net/sched/sch_taprio.c:992
 __run_hrtimer kernel/time/hrtimer.c:2032 [inline]
 __hrtimer_run_queues+0x3bc/0xa10 kernel/time/hrtimer.c:2096
 hrtimer_interrupt+0x448/0x910 kernel/time/hrtimer.c:2215
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1051 [inline]
 __sysvec_apic_timer_interrupt+0x102/0x430 arch/x86/kernel/apic/apic.c:1068
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:lru_gen_inc_refs mm/swap.c:442 [inline]
RIP: 0010:folio_mark_accessed+0x2e0/0x8b0 mm/swap.c:501
Code: 84 24 80 00 00 00 0f 85 86 01 00 00 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d e9 56 00 06 ff cc 48 bf 00 00 00 00 80 01 00 00 <4c> 8b 64 24 40 4d 89 e5 49 21 fd 4c 89 ee e8 0d c8 bc ff 48 b8 00
RSP: 0018:ffffc90002edf920 EFLAGS: 00000202
RAX: ffffffff820a3fcb RBX: ffffea00004d6f00 RCX: ffff88801dbd3e00
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000018000000000
RBP: ffffc90002edf9f0 R08: ffffea00004d6f07 R09: 1ffffd400009ade0
R10: dffffc0000000000 R11: fffff9400009ade1 R12: 0000000000000004
R13: dffffc0000000000 R14: 1ffff920005dbf28 R15: 1ffffd400009ade0
 filemap_read+0x61d/0x11e0 mm/filemap.c:2843
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x595/0xa80 fs/read_write.c:574
 ksys_read+0x150/0x270 fs/read_write.c:716
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa1a8600134
Code: 48 3d 00 f0 ff ff 77 06 c3 0f 1f 44 00 00 f7 d8 89 05 80 41 01 00 48 c7 c0 ff ff ff ff c3 0f 1f 84 00 00 00 00 00 31 c0 0f 05 <48> 3d 00 f0 ff ff 77 04 c3 0f 1f 00 f7 d8 89 05 58 41 01 00 48 c7
RSP: 002b:00007ffe14a46718 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007ffe14a46790 RCX: 00007fa1a8600134
RDX: 0000000000000340 RSI: 00007ffe14a469a8 RDI: 0000000000000000
RBP: 00007ffe14a46780 R08: 00007ffe14a46987 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000340 R14: 00007ffe14a469a0 R15: 00007ffe14a469a8
 </TASK>
rcu: rcu_preempt kthread starved for 10494 jiffies! g18401 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:27496 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x17d9/0x56c0 kernel/sched/core.c:7234
 __schedule_loop kernel/sched/core.c:7311 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7326
 schedule_timeout+0x152/0x2c0 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x30c/0x11f0 kernel/rcu/tree.c:2123
 rcu_gp_kthread+0x9e/0x2b0 kernel/rcu/tree.c:2325
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 UID: 0 PID: 3319 Comm: kworker/u8:8 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: events_unbound toggle_allocation_gate
RIP: 0010:csd_lock_wait kernel/smp.c:342 [inline]
RIP: 0010:smp_call_function_many_cond+0x11eb/0x15f0 kernel/smp.c:912
Code: 1e 89 de 83 e6 01 31 ff e8 e2 22 0c 00 83 e3 01 48 bb 00 00 00 00 00 fc ff df 75 07 e8 8e 1e 0c 00 eb 37 f3 90 41 0f b6 04 1c <84> c0 75 10 41 f7 06 01 00 00 00 74 1e e8 73 1e 0c 00 eb e5 44 89
RSP: 0018:ffffc9000db97700 EFLAGS: 00000293
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffff888032c90000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc9000db97860 R08: ffffffff90579137 R09: 1ffffffff20af226
R10: dffffc0000000000 R11: fffffbfff20af227 R12: 1ffff110170e81d1
R13: ffff8880b863c448 R14: ffff8880b8740e88 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888124f4e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7fdb89a000 CR3: 000000000e946000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 on_each_cpu_cond_mask+0x3f/0x80 kernel/smp.c:1077
 on_each_cpu include/linux/smp.h:72 [inline]
 smp_text_poke_sync_each_cpu arch/x86/kernel/alternative.c:2773 [inline]
 smp_text_poke_batch_finish+0x5fd/0x1110 arch/x86/kernel/alternative.c:2983
 arch_jump_label_transform_apply+0x1c/0x30 arch/x86/kernel/jump_label.c:146
 static_key_enable_cpuslocked+0x128/0x240 kernel/jump_label.c:210
 static_key_enable+0x1a/0x20 kernel/jump_label.c:223
 toggle_allocation_gate+0xab/0x290 mm/kfence/core.c:911
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


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