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From: Linus Torvalds <torvalds@linux-foundation.org>
To: John Stultz <john.stultz@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	"Krzysztof Hałasa" <khalasa@piap.pl>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Willy Tarreau" <w@1wt.eu>, "Ingo Molnar" <mingo@kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Stephen Boyd" <sboyd@codeaurora.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] sched_clock: Disable seqlock lockdep usage in sched_clock
Date: Thu, 2 Jan 2014 14:15:08 -0800	[thread overview]
Message-ID: <CA+55aFxGQkChbFj=GMWAANmbJ512S5KAcFNvKoQJsQCiMfvxqA@mail.gmail.com> (raw)
In-Reply-To: <1388699686-4834-1-git-send-email-john.stultz@linaro.org>

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.

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.

             Linus

WARNING: multiple messages have this Message-ID (diff)
From: torvalds@linux-foundation.org (Linus Torvalds)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] sched_clock: Disable seqlock lockdep usage in sched_clock
Date: Thu, 2 Jan 2014 14:15:08 -0800	[thread overview]
Message-ID: <CA+55aFxGQkChbFj=GMWAANmbJ512S5KAcFNvKoQJsQCiMfvxqA@mail.gmail.com> (raw)
In-Reply-To: <1388699686-4834-1-git-send-email-john.stultz@linaro.org>

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.

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.

             Linus

  reply	other threads:[~2014-01-02 22:15 UTC|newest]

Thread overview: 52+ 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 10:37 ` Krzysztof Hałasa
2013-12-31 10:45 ` Willy Tarreau
2013-12-31 10:45   ` Willy Tarreau
2014-01-02 10:02   ` Krzysztof Hałasa
2014-01-02 10:02     ` Krzysztof Hałasa
2014-01-02 10:14     ` Uwe Kleine-König
2014-01-02 10:14       ` Uwe Kleine-König
2014-01-02 12:07       ` Krzysztof Hałasa
2014-01-02 12:07         ` Krzysztof Hałasa
2014-01-02 19:38         ` Linus Torvalds
2014-01-02 19:38           ` Linus Torvalds
2014-01-02 20:03           ` John Stultz
2014-01-02 20:03             ` John Stultz
2014-01-02 20:30             ` John Stultz
2014-01-02 20:30               ` John Stultz
2014-01-02 20:42               ` Stephen Boyd
2014-01-02 20:42                 ` Stephen Boyd
2014-01-02 20:52                 ` John Stultz
2014-01-02 20:52                   ` John Stultz
2014-01-02 20:43               ` Linus Torvalds
2014-01-02 20:43                 ` Linus Torvalds
2014-01-02 21:34                 ` John Stultz
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 21:54                     ` John Stultz
2014-01-02 22:15                     ` Linus Torvalds [this message]
2014-01-02 22:15                       ` Linus Torvalds
2014-01-02 22:21                       ` John Stultz
2014-01-02 22:21                         ` John Stultz
2014-01-02 23:11                         ` [PATCH 1/2] seqlock: Use raw_ prefix instead of _no_lockdep John Stultz
2014-01-02 23:11                           ` John Stultz
2014-01-02 23:11                           ` [PATCH 2/2] sched_clock: Disable seqlock lockdep usage in sched_clock John Stultz
2014-01-02 23:11                             ` John Stultz
2014-01-03  0:46                             ` Stephen Boyd
2014-01-03  0:46                               ` Stephen Boyd
2014-01-03  6:05                             ` Krzysztof Hałasa
2014-01-03  6:05                               ` Krzysztof Hałasa
2014-01-12 18:42                             ` [tip:core/urgent] sched_clock: Disable seqlock lockdep usage in sched_clock() tip-bot for John Stultz
2014-01-14 19:18                               ` John Stultz
2014-01-15  6:38                                 ` Ingo Molnar
2014-01-03  0:46                           ` [PATCH 1/2] seqlock: Use raw_ prefix instead of _no_lockdep Stephen Boyd
2014-01-03  0:46                             ` Stephen Boyd
2014-01-03  0:50                           ` Linus Torvalds
2014-01-03  0:50                             ` Linus Torvalds
2014-01-04  0:28                             ` John Stultz
2014-01-04  0:28                               ` John Stultz
2014-01-06 10:10                               ` Peter Zijlstra
2014-01-06 10:10                                 ` Peter Zijlstra
2014-01-12 18:42                           ` [tip:core/urgent] " tip-bot for John Stultz
2014-01-03  6:01           ` v3.13-rc6+ regression (ARM board) Krzysztof Hałasa
2014-01-03  6:01             ` Krzysztof Hałasa

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