INFO: rcu detected stall in ext4_write_checks

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    abf02e29 Merge tag 'pm-5.2-rc6' of git://git.kernel.org/pu..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1435aaf6a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e5c77f8090a3b96b
dashboard link: https://syzkaller.appspot.com/bug?extid=4bfbbf28a2e50ab07368
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11234c41a00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15d7f026a00000

The bug was bisected to:

commit 0c81ea5db25986fb2a704105db454a790c59709c
Author: Elad Raz <eladr@xxxxxxxxxxxx>
Date:   Fri Oct 28 19:35:58 2016 +0000

    mlxsw: core: Add port type (Eth/IB) set API

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10393a89a00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=12393a89a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=14393a89a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4bfbbf28a2e50ab07368@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 0c81ea5db259 ("mlxsw: core: Add port type (Eth/IB) set API")

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
	(detected by 0, t=10502 jiffies, g=8969, q=26)
rcu: All QSes seen, last rcu_preempt kthread activity 10503  
(4295056736-4295046233), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor778 R  running task    26464  9577   9576 0x00004000
Call Trace:
 <IRQ>
 sched_show_task kernel/sched/core.c:5286 [inline]
 sched_show_task.cold+0x291/0x2fc kernel/sched/core.c:5261
 print_other_cpu_stall kernel/rcu/tree_stall.h:410 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:536 [inline]
 rcu_pending kernel/rcu/tree.c:2625 [inline]
 rcu_sched_clock_irq.cold+0xaaf/0xbfd kernel/rcu/tree.c:2161
 update_process_times+0x32/0x80 kernel/time/timer.c:1639
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:167
 tick_sched_timer+0x47/0x130 kernel/time/tick-sched.c:1298
 __run_hrtimer kernel/time/hrtimer.c:1389 [inline]
 __hrtimer_run_queues+0x33b/0xdd0 kernel/time/hrtimer.c:1451
 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1041 [inline]
 smp_apic_timer_interrupt+0x111/0x550 arch/x86/kernel/apic/apic.c:1066
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:806
 </IRQ>
RIP: 0010:ext4_write_checks+0x1/0x260 fs/ext4/file.c:161
Code: 61 fa ff ff e8 e0 3c 53 ff 55 48 89 e5 41 54 49 89 fc e8 f2 0a 81 ff  
4c 89 e7 31 f6 e8 98 f9 ff ff 41 5c 5d c3 0f 1f 40 00 55 <48> 89 e5 41 56  
41 55 49 89 f5 41 54 53 48 89 fb e8 ca 0a 81 ff 48
RSP: 0018:ffff888093a97640 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
RAX: ffff88809901c100 RBX: ffff888093a977d8 RCX: ffffffff81efcb42
RDX: 0000000000000000 RSI: ffff888093a97a08 RDI: ffff888093a977d8
RBP: ffff888093a97768 R08: ffff88809901c100 R09: ffff88809901c9c8
R10: ffff88809901c9a8 R11: ffff88809901c100 R12: 0000000000000001
R13: ffff8880995df4f0 R14: ffff888093a97740 R15: 0000000000000000
 call_write_iter include/linux/fs.h:1872 [inline]
 do_iter_readv_writev+0x5f8/0x8f0 fs/read_write.c:693
 do_iter_write fs/read_write.c:970 [inline]
 do_iter_write+0x184/0x610 fs/read_write.c:951
 vfs_iter_write+0x77/0xb0 fs/read_write.c:983
 iter_file_splice_write+0x65c/0xbd0 fs/splice.c:746
 do_splice_from fs/splice.c:848 [inline]
 direct_splice_actor+0x123/0x190 fs/splice.c:1020
 splice_direct_to_actor+0x366/0x970 fs/splice.c:975
 do_splice_direct+0x1da/0x2a0 fs/splice.c:1063
 do_sendfile+0x597/0xd00 fs/read_write.c:1464
 __do_sys_sendfile64 fs/read_write.c:1519 [inline]
 __se_sys_sendfile64 fs/read_write.c:1511 [inline]
 __x64_sys_sendfile64+0x15a/0x220 fs/read_write.c:1511
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4417c9
Code: e8 7c e7 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 bb 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffce5c38198 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007ffce5c38340 RCX: 00000000004417c9
RDX: 0000000020000000 RSI: 0000000000000003 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 00008080fffffffe R11: 0000000000000246 R12: 0000000000000000
R13: 00000000004024a0 R14: 0000000000000000 R15: 0000000000000000
rcu: rcu_preempt kthread starved for 10549 jiffies! g8969 f0x2  
RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    29056    10      2 0x80004000
Call Trace:
 context_switch kernel/sched/core.c:2818 [inline]
 __schedule+0x7cb/0x1560 kernel/sched/core.c:3445
 schedule+0xa8/0x260 kernel/sched/core.c:3509
 schedule_timeout+0x486/0xc50 kernel/time/timer.c:1807
 rcu_gp_fqs_loop kernel/rcu/tree.c:1589 [inline]
 rcu_gp_kthread+0x9b2/0x18b0 kernel/rcu/tree.c:1746
 kthread+0x354/0x420 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352


---
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