Message-ID: <6871117d.a00a0220.26a83e.004c.GAE@google.com>
Date: Fri, 11 Jul 2025 06:28:29 -0700
From: syzbot <syzbot+5b4f4f81240931b16844@...kaller.appspotmail.com>
To: axboe@...nel.dk, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [mm?] INFO: rcu detected stall in wb_workfn (4)

Hello,

syzbot found the following issue on:

HEAD commit:    d7b8f8e20813 Linux 6.16-rc5
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10a4128c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f51185bd4f40ad44
dashboard link: https://syzkaller.appspot.com/bug?extid=5b4f4f81240931b16844
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f933e0e4a6c5/disk-d7b8f8e2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a82be954c91b/vmlinux-d7b8f8e2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/66dbc3de1264/bzImage-d7b8f8e2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5b4f4f81240931b16844@...kaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P49/2:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=31169, q=1383791 ncpus=2)
task:kworker/u8:3    state:R  running task     stack:21880 pid:49    tgid:49    ppid:2      task_flags:0x24208160 flags:0x00004000
Workqueue: writeback wb_workfn (flush-250:0)
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5401 [inline]
 __schedule+0x116a/0x5de0 kernel/sched/core.c:6790
 preempt_schedule_irq+0x51/0x90 kernel/sched/core.c:7113
 irqentry_exit+0x36/0x90 kernel/entry/common.c:307
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:lock_release+0xa/0x2f0 kernel/locking/lockdep.c:5879
Code: 8b 4c 24 18 4c 8b 54 24 10 44 8b 5c 24 0c eb 8c 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 41 57 41 56 41 55 <41> 54 49 89 f4 53 48 89 fb 48 83 ec 18 65 48 8b 05 f9 07 38 12 48
RSP: 0018:ffffc90000b966d8 EFLAGS: 00000202
RAX: 0000000000000001 RBX: ffffc90000b96bd0 RCX: ffffc90000b98001
RDX: 0000000000000000 RSI: ffffffff816acad4 RDI: ffffffff8e5c4940
RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 000000000000f4f1 R12: ffffc90000b967b8
R13: ffffc90000b96768 R14: ffffc90000b96bd0 R15: ffffc90000b9679c
 rcu_lock_release include/linux/rcupdate.h:341 [inline]
 rcu_read_unlock include/linux/rcupdate.h:871 [inline]
 class_rcu_destructor include/linux/rcupdate.h:1155 [inline]
 unwind_next_frame+0x3f9/0x20a0 arch/x86/kernel/unwind_orc.c:479
 arch_stack_walk+0x94/0x100 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x8e/0xc0 kernel/stacktrace.c:122
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_record_aux_stack+0xa7/0xc0 mm/kasan/generic.c:548
 __call_rcu_common.constprop.0+0xa5/0xa10 kernel/rcu/tree.c:3094
 slab_free_hook mm/slub.c:2345 [inline]
 slab_free mm/slub.c:4643 [inline]
 kmem_cache_free+0x16d/0x4d0 mm/slub.c:4745
 mempool_free+0xe7/0x3b0 mm/mempool.c:548
 bio_put_percpu_cache block/bio.c:801 [inline]
 bio_put+0x355/0x5b0 block/bio.c:820
 bio_endio+0x70a/0x850 block/bio.c:1645
 blk_update_request+0x96b/0x1630 block/blk-mq.c:987
 blk_mq_end_request+0x5b/0x630 block/blk-mq.c:1149
 blk_mq_complete_request block/blk-mq.c:1327 [inline]
 blk_mq_complete_request+0x8b/0xb0 block/blk-mq.c:1324
 nullb_complete_cmd drivers/block/null_blk/main.c:1402 [inline]
 null_handle_cmd drivers/block/null_blk/main.c:1454 [inline]
 null_queue_rq+0xb69/0xfd0 drivers/block/null_blk/main.c:1693
 null_queue_rqs+0xe9/0x2f0 drivers/block/null_blk/main.c:1707
 __blk_mq_flush_list block/blk-mq.c:2826 [inline]
 __blk_mq_flush_list+0x97/0xc0 block/blk-mq.c:2822
 blk_mq_dispatch_queue_requests+0x184/0x7b0 block/blk-mq.c:2871
 blk_mq_flush_plug_list+0x1f2/0x600 block/blk-mq.c:2959
 blk_add_rq_to_plug+0x1ca/0x540 block/blk-mq.c:1388
 blk_mq_submit_bio+0x18d5/0x26a0 block/blk-mq.c:3208
 __submit_bio+0x3cf/0x690 block/blk-core.c:635
 __submit_bio_noacct_mq block/blk-core.c:722 [inline]
 submit_bio_noacct_nocheck+0x660/0xd30 block/blk-core.c:751
 submit_bio_noacct+0x50d/0x1eb0 block/blk-core.c:874
 __block_write_full_folio+0x735/0xe00 fs/buffer.c:1939
 block_write_full_folio+0x341/0x400 fs/buffer.c:2760
 blkdev_writepages+0xb8/0x140 block/fops.c:483
 do_writepages+0x27a/0x600 mm/page-writeback.c:2636
 __writeback_single_inode+0x160/0xfb0 fs/fs-writeback.c:1680
 writeback_sb_inodes+0x601/0xf90 fs/fs-writeback.c:1976
 __writeback_inodes_wb+0xf8/0x2d0 fs/fs-writeback.c:2047
 wb_writeback+0x7f3/0xb70 fs/fs-writeback.c:2158
 wb_check_old_data_flush fs/fs-writeback.c:2262 [inline]
 wb_do_writeback fs/fs-writeback.c:2315 [inline]
 wb_workfn+0x8ca/0xbe0 fs/fs-writeback.c:2343
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
 kthread+0x3c5/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


---
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