linux-kernel - Re: [PATCH] lockdep: Avoid triggering hardlockup from debug_show_all

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Message-ID: <1516734237.31954.17.camel@fb.com>
Date:   Tue, 23 Jan 2018 14:03:57 -0500
From:   Rik van Riel <riel@...com>
To:     Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
        "Ingo Molnar" <mingo@...hat.com>
CC:     <linux-kernel@...r.kernel.org>, <kernel-team@...com>
Subject: Re: [PATCH] lockdep: Avoid triggering hardlockup from
 debug_show_all_locks()

On Mon, 2018-01-22 at 14:00 -0800, Tejun Heo wrote:
> debug_show_all_locks() iterates all tasks and print held locks whole
> holding tasklist_lock.  This can take a while on a slow console
> device
> and may end up triggering NMI hardlockup detector if someone else
> ends
> up waiting for tasklist_lock.
> 
> Touch the NMI watchdog while printing the held locks to avoid
> spuriously triggering the hardlockup detector.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>

On this patch:

Acked-by: Rik van Riel <riel@...riel.com>


However, it seems like we run into things like
this on a fairly regular (though not very frequent)
basis. Would it make sense to go through the code
and add sprinkle around a few more touch_nmi_watchdog()
calls?

After all, there are maybe a few dozen places where
we print out a lot of debugging information.