linux-kernel - Re: ipc,sem: sysv semaphore scalability

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Message-ID: <CA+55aFxjGFi+gt3UwdVCVKP5riHSR=_qLkp0SovgW2zx+gcRow@mail.gmail.com>
Date:	Sat, 23 Mar 2013 12:45:18 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Emmanuel Benisty <benisty.e@...il.com>
Cc:	Rik van Riel <riel@...riel.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, hhuang@...hat.com,
	"Low, Jason" <jason.low2@...com>,
	Michel Lespinasse <walken@...gle.com>,
	Larry Woodman <lwoodman@...hat.com>,
	"Vinod, Chegu" <chegu_vinod@...com>
Subject: Re: ipc,sem: sysv semaphore scalability

On Fri, Mar 22, 2013 at 8:19 PM, Emmanuel Benisty <benisty.e@...il.com> wrote:
>
> I could reproduce it but could you please let me know what would be
> the right tools I should use to catch the original oops?
> This is what I got but I doubt it will be helpful:
> http://i.imgur.com/Mewi1hC.jpg

In this case, I think the best thing to do would be to comment out all
of drm_warn_on_modeset_not_all_locked(), because those warnings make
the original problem (that probably caused the lock problem in the
first place that it is warning about) scroll away.

That said, you should also take the oneliner fix that Rik posted to
patch 7 (subject line: "[PATCH 7/7 part3] fix for sem_lock") and apply
that, just to make sure that you aren't possibly hitting a bug with
the shared-memory locking introduced by that (unusual) case.

                    Linus
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