From: Dave Jones <davej@codemonkey.org.uk>
To: Vegard Nossum <vegard.nossum@oracle.com>
Cc: trinity@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Tejun Heo <tj@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Bjorn Helgaas <bhelgaas@google.com>,
Russell King <rmk+kernel@arm.linux.org.uk>
Subject: Re: cleanup_net()/net_mutex hung tasks + kobject release debugging
Date: Thu, 21 Jul 2016 09:13:46 -0400 [thread overview]
Message-ID: <20160721131346.GA1705@codemonkey.org.uk> (raw)
In-Reply-To: <5790C376.2010206@oracle.com>
On Thu, Jul 21, 2016 at 02:43:34PM +0200, Vegard Nossum wrote:
> The rules for net_mutex are very simple, it's used in very few places so
> I don't see how the locking could get messed up there. I'll buy your
> theory that the lock is held for a long time if there are a lot of
> namespaces to iterate over. I decided to time it myself and it seems
> that cleanup_net() can hold the mutex for 30-40 seconds at a time, which
> is surely wrong.
> so on a hunch I disabled DEBUG_KOBJECT_RELEASE, and that does indeed
> solve the problem -- cleanup_net() still holds the mutex for fairly
> long, but only up to max ~5 seconds at a time as opposed to 30-40.
Yeah, I never ran with that option enabled (it used to cause my testbox
to not boot, and I never got around to debugging why). I thought five seconds
was painful enough. I guess we have different thresholds for acceptable
behaviour here :-)
Could be one of the other debug options I had enabled exacerbates the
cleanup_net problem in a similar way though.
> There's maybe a case for cleanup_net() to release the mutex every now
> and again during cleanup, but I was also seeing a few other hung tasks
> unrelated to net_mutex when I disabled the unshare() system call in
> trinity, which makes me wonder if we need a more general solution.
Not sure. We may have to just look at these on a case by case basis.
Dave
next prev parent reply other threads:[~2016-07-21 13:16 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-21 12:43 cleanup_net()/net_mutex hung tasks + kobject release debugging Vegard Nossum
2016-07-21 13:13 ` Dave Jones [this message]
2016-07-30 12:58 ` Eric W. Biederman
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