From: john.stultz@linaro.org (John Stultz)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] sched_clock: Disable seqlock lockdep usage in sched_clock
Date: Thu, 02 Jan 2014 14:21:41 -0800 [thread overview]
Message-ID: <52C5E675.80701@linaro.org> (raw)
In-Reply-To: <CA+55aFxGQkChbFj=GMWAANmbJ512S5KAcFNvKoQJsQCiMfvxqA@mail.gmail.com>
On 01/02/2014 02:15 PM, Linus Torvalds wrote:
> On Thu, Jan 2, 2014 at 1:54 PM, John Stultz <john.stultz@linaro.org> wrote:
>> Unforunately the seqlock lockdep enablmenet can't be used
>> in sched_clock, since the lockdep infrastructure eventually
>> calls into sched_clock, which causes a deadlock.
>>
>> Thus, this patch adds _no_lockdep() seqlock methods for the
>> writer side, and changes all generic sched_clock usage to use
>> the _no_lockdep methods.
> Ugh.
>
> On the x86 vclock_gettime() side, we only do this for the reader. Why
> did you make the generic version do it for the writer too, adding the
> necessity for those new operations? It's only the reader side that
> doesn't want it.
So the problem is that the update side calls the lockdep code which
calls sched_clock, which then deadlocks because the seqcount is odd
(held by the updater).
Thus we have to drop the lockdep usage in the updater as well.
On x86 vclock_gettime, we're in userspace, and that's why we can't call
the lockdep code. The update for that code however happens in kernel
space, so it doesn't have the same problem.
> Talking about the new operations, that "*_no_lockdep()" naming annoys
> me. It doesn't match the spinlock naming, which is to just use
> "raw_*()" instead. Wouldn't it be nice to make the naming be
> consistent too? Especially when it's paired with raw_local_irq_save()
> that shares that "raw_" model for non-checking stuff.
Sure, I can change the naming. New patch to follow in a bit.
thanks
-john
next prev parent reply other threads:[~2014-01-02 22:21 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-31 10:37 v3.13-rc6+ regression (ARM board) Krzysztof Hałasa
2013-12-31 10:45 ` Willy Tarreau
2014-01-02 10:02 ` Krzysztof Hałasa
2014-01-02 10:14 ` Uwe Kleine-König
2014-01-02 12:07 ` Krzysztof Hałasa
2014-01-02 19:38 ` Linus Torvalds
2014-01-02 20:03 ` John Stultz
2014-01-02 20:30 ` John Stultz
2014-01-02 20:42 ` Stephen Boyd
2014-01-02 20:52 ` John Stultz
2014-01-02 20:43 ` Linus Torvalds
2014-01-02 21:34 ` John Stultz
2014-01-02 21:54 ` [PATCH] sched_clock: Disable seqlock lockdep usage in sched_clock John Stultz
2014-01-02 22:15 ` Linus Torvalds
2014-01-02 22:21 ` John Stultz [this message]
2014-01-02 23:11 ` [PATCH 1/2] seqlock: Use raw_ prefix instead of _no_lockdep John Stultz
2014-01-02 23:11 ` [PATCH 2/2] sched_clock: Disable seqlock lockdep usage in sched_clock John Stultz
2014-01-03 0:46 ` Stephen Boyd
2014-01-03 6:05 ` Krzysztof Hałasa
2014-01-03 0:46 ` [PATCH 1/2] seqlock: Use raw_ prefix instead of _no_lockdep Stephen Boyd
2014-01-03 0:50 ` Linus Torvalds
2014-01-04 0:28 ` John Stultz
2014-01-06 10:10 ` Peter Zijlstra
2014-01-03 6:01 ` v3.13-rc6+ regression (ARM board) Krzysztof Hałasa
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