Re: How to decode output from sysrq - t

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On Mon, 11 Feb 2013, Staffan Tjernstrom wrote:

> I'm trying to plow through the output from sysrq - t on a system
> where I think we may have a rouge high-priority call to the file
> system from userspace causing a priority inversion issue.

Abby hangs in a futex_wait() which has nothing to do with file
systems.

> For the particular instance I'm looking at, it would appear that the
> "other" half of the hang is the auditd daemon.

Well, there is no indication that auditd blocks on the same futex as
Abby and I really would wonder if that's the case.

> My question is this - is the format of the output between the task
> name and the call trace documented anywhere? Or where in the code
> should I look for it?

> auditd          S ffff880418b967c0     0  2998      1 0x00000000

sched_show_task()

>  ffff880418479bf8 0000000000000086 00000000000000d0 ffff880418478000
>  ffff880418478010 ffff880418478010 ffff880418479fd8 ffff880418478000
>  ffff880418478000 ffff880418478000 ffff88041e3380c0 ffff880418b96400

show_stack()

> Call Trace:
>  [<ffffffff814e1aae>] schedule+0x2e/0xa0
>  [<ffffffff810898dc>] futex_wait_queue_me+0xcc/0x110
>  [<ffffffff81089ba5>] futex_wait+0x195/0x290
>  [<ffffffff8104b4fb>] ? migrate_enable+0xdb/0x1d0
>  [<ffffffff810892a6>] ? futex_wake+0x126/0x140
>  [<ffffffff8108ab34>] do_futex+0x124/0xaf0
>  [<ffffffff8104b4fb>] ? migrate_enable+0xdb/0x1d0
>  [<ffffffffa019463f>] ? ext2_statfs+0xef/0x180 [ext2]
>  [<ffffffff8117c388>] ? do_statfs_native+0x98/0xb0
>  [<ffffffff8108b57b>] sys_futex+0x7b/0x170
>  [<ffffffff814eab2b>] system_call_fastpath+0x16/0x1b
> 
> Abby            S ffff8804181849c0     0 30761  30740 0x00000080
>  ffff880418ac9bf8 0000000000000086 ffff880400000000 ffff880418ac8000
>  ffff880418ac8010 ffff880418ac8010 ffff880418ac9fd8 ffff880418ac8000
>  ffff880418ac8000 ffff880418ac8000 ffffffff81a10020 ffff880418184600
> Call Trace:
>  [<ffffffff814e1aae>] schedule+0x2e/0xa0
>  [<ffffffff810898dc>] futex_wait_queue_me+0xcc/0x110
>  [<ffffffff81089ba5>] futex_wait+0x195/0x290
>  [<ffffffff81079410>] ? update_rmtp+0x80/0x80
>  [<ffffffff8108ab34>] do_futex+0x124/0xaf0
>  [<ffffffff8114b5ca>] ? do_sync_write+0xea/0x130
>  [<ffffffff8114cc57>] ? fget_light+0x97/0xf0
>  [<ffffffff8118a7ea>] ? fsnotify+0x1ea/0x320
>  [<ffffffff8108b57b>] sys_futex+0x7b/0x170
>  [<ffffffff814eab2b>] system_call_fastpath+0x16/0x1b

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