syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P3476/1:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=11601, q=814 ncpus=2)
task:kworker/u4:8    state:R  running task     stack:20648 pid:3476  ppid:2      flags:0x00004000
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7010
 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:instrument_atomic_read include/linux/instrumented.h:68 [inline]
RIP: 0010:atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
RIP: 0010:folio_memcg_lock+0x1c8/0x320 mm/memcontrol.c:2165
Code: 00 9c 8f 44 24 60 f7 44 24 60 00 02 00 00 c6 44 03 08 f8 0f 85 8d 00 00 00 41 f7 c5 00 02 00 00 74 01 fb 4d 8d a7 40 09 00 00 <4c> 89 e7 be 04 00 00 00 e8 fb e7 f8 ff 4c 89 e0 48 c1 e8 03 48 b9
RSP: 0018:ffffc9000d1aeaa0 EFLAGS: 00000206
RAX: dffffc0000000000 RBX: 1ffff92001a35d58 RCX: 0888a8394e1d5e00
RDX: dffffc0000000000 RSI: ffffffff8acac960 RDI: ffffffff8b1c85a0
RBP: ffffc9000d1aeb70 R08: ffffffff911c15a7 R09: 1ffffffff22382b4
R10: dffffc0000000000 R11: fffffbfff22382b5 R12: ffff88814125a940
R13: 0000000000000286 R14: 1ffff92001a35d58 R15: ffff88814125a000
 __folio_start_writeback+0x163/0xfe0 mm/page-writeback.c:3017
 ext4_bio_write_folio+0xed8/0x2240 fs/ext4/page-io.c:566
 mpage_submit_folio+0x237/0x3c0 fs/ext4/inode.c:1908
 mpage_map_and_submit_buffers fs/ext4/inode.c:2154 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2293 [inline]
 ext4_do_writepages+0x1d5c/0x3990 fs/ext4/inode.c:2718
 ext4_writepages+0x1dd/0x350 fs/ext4/inode.c:2807
 do_writepages+0x3b3/0x630 mm/page-writeback.c:2575
 __writeback_single_inode+0x153/0xec0 fs/fs-writeback.c:1635
 writeback_sb_inodes+0x7cd/0xf50 fs/fs-writeback.c:1926
 __writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:1997
 wb_writeback+0x47e/0xbf0 fs/fs-writeback.c:2107
 wb_check_old_data_flush fs/fs-writeback.c:2211 [inline]
 wb_do_writeback fs/fs-writeback.c:2264 [inline]
 wb_workfn+0xad7/0xe60 fs/fs-writeback.c:2292
 process_one_work kernel/workqueue.c:2653 [inline]
 process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2730
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2811
 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: rcu_preempt kthread starved for 10546 jiffies! g11601 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:27720 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_timeout+0x188/0x2d0 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x313/0x1590 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: 5958 Comm: syz.2.27 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:entry_SYSCALL_64_after_hwframe+0x59/0xd2
Code: 45 31 e4 45 31 ed 45 31 f6 45 31 ff 48 89 e7 48 63 f0 66 90 b9 48 00 00 00 65 48 8b 14 25 60 7f 02 00 89 d0 48 c1 ea 20 0f 30 <0f> 1f 44 00 00 e8 d5 19 00 00 e8 90 cb e4 ff 0f 1f 44 00 00 48 8b
RSP: 0018:ffffc90003567f58 EFLAGS: 00000046
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000048
RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffffc90003567f58
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007fd85d89a6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000058 CR3: 0000000076c8b000 CR4: 00000000003506f0
Call Trace:
 <TASK>
RIP: 0033:0x7fd85c996517
Code: 8d 3d 04 8e 0b 00 e8 58 1d fa ff e8 a3 87 00 00 0f 1f 00 b8 68 00 00 00 0f 05 c3 0f 1f 84 00 00 00 00 00 b8 27 00 00 00 0f 05 <c3> 0f 1f 84 00 00 00 00 00 b8 6e 00 00 00 0f 05 c3 0f 1f 84 00 00
RSP: 002b:00007fd85d899b08 EFLAGS: 00000202 ORIG_RAX: 0000000000000027
RAX: ffffffffffffffda RBX: 00007fd85d899c70 RCX: 00007fd85c996517
RDX: 00007fd85d899b40 RSI: 00007fd85d899c70 RDI: 0000000000000021
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007fd85cc16038 R14: 00007ffd04f974c0 R15: 00007ffd04f975a8
 </TASK>
sched: RT throttling activated