linux-kernel - hung_task checking and sys

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Date:	Tue, 12 Jun 2012 15:09:24 -0700
From:	Daniel Walker <dwalker@...o99.com>
To:	fweisbec@...il.com
Cc:	msb@...omium.org, sshaiju@...sta.com, mingo@...e.hu,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: hung_task checking and sys_sync


I found this commit which was a while ago,

commit fb822db465bd9fd4208eef1af4490539b236c54e
Author: Ingo Molnar <mingo@...e.hu>
Date:   Wed Aug 20 11:17:40 2008 +0200

    softlockup: increase hung tasks check from 2 minutes to 8 minutes
    
    Andrew says:
    
    > Seems that about 100% of the reports we get of this warning triggering
    > are sys_sync, transaction commit, etc.
    
    increase the timeout. If it still triggers for people, we can kill it.
    
    Signed-off-by: Ingo Molnar <mingo@...e.hu>


We're seeing these messages on an older kernel (montavista) but the code areas
appear similar to current kernels. The issue is that we're doing a file copy
which takes 10-15minutes, and in the background there is a "df --sync"
happening (which is calling sys_sync). We end up getting a hung task message
like below,

INFO: task df:1778 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
ffffffff81578d40 0000000000000086 ffff8801f6135b00 ffff880269a91800
ffff880269a91800 ffff8802702be000 ffff8801f602a080 0000000000000000
ffff8801f602a440 ffffffff8109c166 ffff8801e863de18 0000000000000004
Call Trace:
  [<ffffffff8109c166>] ? sync_page+0x0/0x49
  [<ffffffff81320de2>] ? __schedule+0x3c/0x57
  [<ffffffff810ea3c7>] ? bdi_sched_wait+0x0/0xe
  [<ffffffff81320de2>] ? __schedule+0x3c/0x57
  [<ffffffff81320e0d>] ? schedule+0x10/0x1e
  [<ffffffff810ea3d0>] ? bdi_sched_wait+0x9/0xe

There some variation in the stack trace , but always thru bdi_sched_wait().


These don't seem like valid warnings, since the copy happening is know to take
a long time. Has there been any commit that disable these messages bdi_sched_wait?

Daniel
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