INFO: rcu detected stall in wb_workfn

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3f8a27f9e27b Linux 4.19.211
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16a7627b080000
kernel config: https://syzkaller.appspot.com/x/.config?x=9b9277b418617afe
dashboard link: https://syzkaller.appspot.com/bug?extid=04e0352bad01d2d688bc
compiler: gcc version 10.2.1 20210110 (Debian 10.2.1-6)

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+04e035...@syzkaller.appspotmail.com

Bluetooth: hci5: command 0x0406 tx timeout
Bluetooth: hci3: command 0x0406 tx timeout
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: (detected by 0, t=10502 jiffies, g=35665, q=2495)
rcu: All QSes seen, last rcu_preempt kthread activity 10503 (4294976912-4294966409), jiffies_till_next_fqs=1, root ->qsmask 0x0
kworker/u4:10 R running task 25664 9811 2 0x80000000
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
<IRQ>
sched_show_task.cold+0x332/0x396 kernel/sched/core.c:5337
print_other_cpu_stall kernel/rcu/tree.c:1430 [inline]
check_cpu_stall kernel/rcu/tree.c:1557 [inline]
__rcu_pending kernel/rcu/tree.c:3293 [inline]
rcu_pending kernel/rcu/tree.c:3336 [inline]
rcu_check_callbacks.cold+0xb37/0xe19 kernel/rcu/tree.c:2682
update_process_times+0x2a/0x70 kernel/time/timer.c:1650
tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:168
tick_sched_timer+0xfc/0x290 kernel/time/tick-sched.c:1278
__run_hrtimer kernel/time/hrtimer.c:1465 [inline]
__hrtimer_run_queues+0x3f6/0xe60 kernel/time/hrtimer.c:1527
hrtimer_interrupt+0x326/0x9e0 kernel/time/hrtimer.c:1585
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1071 [inline]
smp_apic_timer_interrupt+0x10c/0x550 arch/x86/kernel/apic/apic.c:1096
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:894
</IRQ>
RIP: 0010:arch_atomic_try_cmpxchg arch/x86/include/asm/atomic.h:200 [inline]
RIP: 0010:atomic_try_cmpxchg include/asm-generic/atomic-instrumented.h:73 [inline]
RIP: 0010:__pv_queued_spin_lock_slowpath+0x7b7/0xae0 kernel/locking/qspinlock.c:498
Code: df 48 c1 ea 03 0f b6 04 02 3c 03 7f 0c 84 c0 74 08 4c 89 ef e8 fa c3 4c 00 8b 44 24 60 ba 01 00 00 00 89 04 24 f0 0f b1 55 00 <0f> 84 76 fa ff ff 48 ba 00 00 00 00 00 fc ff df 4c 89 e9 48 c1 e9
RSP: 0018:ffff888058686cc8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000040001 RBX: 0000000000000000 RCX: ffffffff814b9db1
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffff888058686d28
RBP: ffff888235104cc0 R08: 0000000000000000 R09: ffffed100b0d0da5
R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000000000
R13: ffff888058686d28 R14: 0000000000000001 R15: ffff8880ba02be00
pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:679 [inline]
queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:53 [inline]
queued_spin_lock include/asm-generic/qspinlock.h:88 [inline]
do_raw_spin_lock+0x189/0x220 kernel/locking/spinlock_debug.c:113
spin_lock include/linux/spinlock.h:329 [inline]
ext4_lock_group fs/ext4/ext4.h:3022 [inline]
ext4_mb_discard_group_preallocations+0xada/0x12c0 fs/ext4/mballoc.c:3943
ext4_mb_discard_preallocations fs/ext4/mballoc.c:4478 [inline]
ext4_mb_new_blocks+0x1d1d/0x4370 fs/ext4/mballoc.c:4593
ext4_ext_map_blocks+0x2aa2/0x7390 fs/ext4/extents.c:4493
ext4_map_blocks+0x7a2/0x1a50 fs/ext4/inode.c:657
mpage_map_one_extent fs/ext4/inode.c:2477 [inline]
mpage_map_and_submit_extent fs/ext4/inode.c:2530 [inline]
ext4_writepages+0x1d1d/0x37f0 fs/ext4/inode.c:2882
do_writepages+0xe5/0x290 mm/page-writeback.c:2344
__writeback_single_inode+0x10c/0x11d0 fs/fs-writeback.c:1385
writeback_sb_inodes+0x537/0xef0 fs/fs-writeback.c:1647
__writeback_inodes_wb+0xc6/0x280 fs/fs-writeback.c:1716
wb_writeback+0x841/0xcc0 fs/fs-writeback.c:1822
wb_check_old_data_flush fs/fs-writeback.c:1924 [inline]
wb_do_writeback fs/fs-writeback.c:1977 [inline]
wb_workfn+0x8ba/0x1250 fs/fs-writeback.c:2006
process_one_work+0x864/0x1570 kernel/workqueue.c:2153
worker_thread+0x64c/0x1130 kernel/workqueue.c:2296
kthread+0x33f/0x460 kernel/kthread.c:259
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
rcu: rcu_preempt kthread starved for 10545 jiffies! g35665 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt R running task 29016 10 2 0x80000000
Call Trace:
context_switch kernel/sched/core.c:2828 [inline]
__schedule+0x887/0x2040 kernel/sched/core.c:3517
schedule+0x8d/0x1b0 kernel/sched/core.c:3561
schedule_timeout+0x4cf/0xfe0 kernel/time/timer.c:1818
rcu_gp_kthread+0xdad/0x21c0 kernel/rcu/tree.c:2202
kthread+0x33f/0x460 kernel/kthread.c:259
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.