linux-kernel - Re: INFO: rcu detected stall in sys

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Date:   Sat, 19 Jan 2019 12:41:17 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+1505c80c74256c6118a5@...kaller.appspotmail.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Amir Goldstein <amir73il@...il.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dave Chinner <david@...morbit.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hugh Dickins <hughd@...gle.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: INFO: rcu detected stall in sys_sendfile64 (2)

On Sat, Jan 19, 2019 at 12:32 PM syzbot
<syzbot+1505c80c74256c6118a5@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    2339e91d0e66 Merge tag 'media/v5.0-1' of git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=175f2638c00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=abc3dc9b7a900258
> dashboard link: https://syzkaller.appspot.com/bug?extid=1505c80c74256c6118a5
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12c4dc28c00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15df4108c00000

Looking at the reproducer it looks like something with scheduler as it
involves perf_event_open and sched_setattr. So +Peter and Mingo.
Is it the same root cause as the other stalls involving sched_setattr?

> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+1505c80c74256c6118a5@...kaller.appspotmail.com
>
> audit: type=1400 audit(1547895693.874:36): avc:  denied  { map } for
> pid=8427 comm="syz-executor786" path="/root/syz-executor786610373"
> dev="sda1" ino=1426 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
> tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
> hrtimer: interrupt took 42996 ns
> rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> rcu:    (detected by 0, t=10502 jiffies, g=6469, q=3)
> rcu: All QSes seen, last rcu_preempt kthread activity 10502
> (4295051508-4295041006), jiffies_till_next_fqs=1, root ->qsmask 0x0
> syz-executor786 R  running task    21544  8437   8433 0x00000000
> Call Trace:
>   <IRQ>
>   sched_show_task kernel/sched/core.c:5293 [inline]
>   sched_show_task.cold+0x273/0x2d5 kernel/sched/core.c:5268
>   print_other_cpu_stall.cold+0x7f2/0x8bb kernel/rcu/tree.c:1301
>   check_cpu_stall kernel/rcu/tree.c:1429 [inline]
>   rcu_pending kernel/rcu/tree.c:3018 [inline]
>   rcu_check_callbacks+0xf36/0x1380 kernel/rcu/tree.c:2521
>   update_process_times+0x32/0x80 kernel/time/timer.c:1635
>   tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:161
>   tick_sched_timer+0x47/0x130 kernel/time/tick-sched.c:1271
>   __run_hrtimer kernel/time/hrtimer.c:1389 [inline]
>   __hrtimer_run_queues+0x3a7/0x1050 kernel/time/hrtimer.c:1451
>   hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509
>   local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1035 [inline]
>   smp_apic_timer_interrupt+0x18d/0x760 arch/x86/kernel/apic/apic.c:1060
>   apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807
>   </IRQ>
> RIP: 0010:preempt_count arch/x86/include/asm/preempt.h:26 [inline]
> RIP: 0010:check_kcov_mode kernel/kcov.c:67 [inline]
> RIP: 0010:write_comp_data+0x9/0x70 kernel/kcov.c:122
> Code: 12 00 00 8b 80 dc 12 00 00 48 8b 11 48 83 c2 01 48 39 d0 76 07 48 89
> 34 d1 48 89 11 5d c3 0f 1f 00 65 4c 8b 04 25 40 ee 01 00 <65> 8b 05 80 ee
> 7f 7e a9 00 01 1f 00 75 51 41 8b 80 d8 12 00 00 83
> RSP: 0018:ffff888080466f58 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
> RAX: 000000000000226d RBX: ffff888080467140 RCX: ffffffff87f08bdf
> RDX: 0000000000000002 RSI: 0000000000000002 RDI: 0000000000000007
> RBP: ffff888080466f60 R08: ffff888096338480 R09: ffffed1015cc5b90
> R10: ffffed1015cc5b8f R11: ffff8880ae62dc7b R12: 1ffff1101008cdf0
> R13: ffff888092b64102 R14: ffff888092b64102 R15: ffff888080467158
>   xa_is_node include/linux/xarray.h:946 [inline]
>   xas_start+0x1cf/0x720 lib/xarray.c:183
>   xas_load+0x21/0x160 lib/xarray.c:227
>   find_get_entry+0x350/0x10a0 mm/filemap.c:1476
>   pagecache_get_page+0xe6/0x1020 mm/filemap.c:1579
>   find_get_page include/linux/pagemap.h:272 [inline]
>   generic_file_buffered_read mm/filemap.c:2076 [inline]
>   generic_file_read_iter+0x7b2/0x2d40 mm/filemap.c:2350
>   ext4_file_read_iter+0x180/0x3c0 fs/ext4/file.c:77
>   call_read_iter include/linux/fs.h:1856 [inline]
>   generic_file_splice_read+0x5c4/0xa90 fs/splice.c:308
>   do_splice_to+0x12a/0x190 fs/splice.c:880
>   splice_direct_to_actor+0x31b/0x9d0 fs/splice.c:957
>   do_splice_direct+0x2c7/0x420 fs/splice.c:1066
>   do_sendfile+0x61a/0xe60 fs/read_write.c:1436
>   __do_sys_sendfile64 fs/read_write.c:1491 [inline]
>   __se_sys_sendfile64 fs/read_write.c:1483 [inline]
>   __x64_sys_sendfile64+0x15a/0x240 fs/read_write.c:1483
>   do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x446a19
> Code: e8 dc e6 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 4b 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f53e33cfda8 EFLAGS: 00000297 ORIG_RAX: 0000000000000028
> RAX: ffffffffffffffda RBX: 00000000006dcc28 RCX: 0000000000446a19
> RDX: 0000000020000380 RSI: 0000000000000003 RDI: 0000000000000003
> RBP: 00000000006dcc20 R08: 0000000000000000 R09: 0000000000000000
> R10: 00008080fffffffe R11: 0000000000000297 R12: 00000000006dcc2c
> R13: 00008080fffffffe R14: 00007f53e33d09c0 R15: 00000000006dcd2c
> rcu: rcu_preempt kthread starved for 10502 jiffies! g6469 f0x2
> RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
> rcu: RCU grace-period kthread stack dump:
> rcu_preempt     R  running task    26200    10      2 0x80000000
> Call Trace:
>   context_switch kernel/sched/core.c:2831 [inline]
>   __schedule+0x897/0x1e60 kernel/sched/core.c:3472
>   schedule+0xfe/0x350 kernel/sched/core.c:3516
>   schedule_timeout+0x14a/0x250 kernel/time/timer.c:1803
>   rcu_gp_fqs_loop+0x6ba/0x970 kernel/rcu/tree.c:1948
>   rcu_gp_kthread+0x2bb/0xc10 kernel/rcu/tree.c:2105
>   kthread+0x357/0x430 kernel/kthread.c:246
>   ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
> sched: RT throttling activated
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
> syzbot can test patches for this bug, for details see:
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>
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