linux-kernel - Re: hung_task checking and sys

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Date:	Tue, 12 Jun 2012 15:34:22 -0700
From:	Daniel Walker <dwalker@...o99.com>
To:	Mandeep Singh Baines <msb@...gle.com>
Cc:	fweisbec@...il.com, msb@...omium.org, sshaiju@...sta.com,
	mingo@...e.hu, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: hung_task checking and sys_sync

On Tue, Jun 12, 2012 at 03:29:12PM -0700, Mandeep Singh Baines wrote:
> 
> But the time is not unbounded. You could mask the hung_task_detector for
> this case but then you lose the ability to catch bugs in this code path.
> 
> The timeout is configurable via /proc/sys/kernel/hung_task_timeout_secs.
> Can you bump up the value at boot via sysctl.conf?

Maybe, but I'm wondering if these types should just be stopped because Andrew
had complained about them already.
 
> > Has there been any commit that disable these messages bdi_sched_wait?
> > 
> 
> No. There is no mechanism to disable hung_task for a specific code path.
> We do skip processes if PF_PROZEN or PF_FROZEN_SKIP is set but that is
> really a different situation where the wait is unbounded.

There is presidence for this type of change, 

Author: Mark Lord <kernel@...savvy.com>
Date:   Fri Sep 24 09:51:13 2010 -0400

    block: Prevent hang_check firing during long I/O
    
    During long I/O operations, the hang_check timer may fire,
    trigger stack dumps that unnecessarily alarm the user.
    
    Eg.  hdparm --security-erase NULL /dev/sdb  ## can take *hours* to complete
    
    So, if hang_check is armed, we should wake up periodically
    to prevent it from triggering.  This patch uses a wake-up interval
    equal to half the hang_check timer period, which keeps overhead low enough.
    
    Signed-off-by: Mark Lord <mlord@...ox.com>
    Signed-off-by: Jens Axboe <jaxboe@...ionio.com>

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