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    SubjectRE: hung_task checking and sys_sync
    There   was  another  patch   addressing  these  type  of  issue .

    https://lkml.org/lkml/2009/1/12/18


    regards,
    shaiju.

    -----Original Message-----
    From: Mandeep Baines [mailto:msb@google.com]
    Sent: Tuesday, June 12, 2012 3:45 PM
    To: Daniel Walker
    Cc: fweisbec@gmail.com; sshaiju@mvista.com; mingo@elte.hu;
    akpm@linux-foundation.org; linux-kernel@vger.kernel.org
    Subject: Re: hung_task checking and sys_sync

    On Tue, Jun 12, 2012 at 3:34 PM, Daniel Walker <dwalker@fifo99.com> wrote:
    > 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.
    >

    Fair enough. Actually, internally I had a patch where we'd use a task flag
    to disable and enable the hang check but the approach in the patch you
    pointed me to seems better.

    >> > 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@teksavvy.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@pobox.com>
    >    Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
    >

    Interesting. I wasn't aware of this patch. Maybe we could abstract this
    approach via wait_for_completion_no_hang_check().

    Regards,
    Mandeep
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