From: pdeschrijver@nvidia•com (Peter De Schrijver)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] clk: Fix race conditions between clk_set_parent() and clk_enable()
Date: Tue, 22 May 2012 16:58:13 +0300 [thread overview]
Message-ID: <20120522135813.GL8730@tbergstrom-lnx.Nvidia.com> (raw)
In-Reply-To: <4FB29E7C.7010606@codeaurora.org>
On Tue, May 15, 2012 at 08:20:44PM +0200, Saravana Kannan wrote:
> On 05/11/2012 09:59 PM, Saravana Kannan wrote:
> > Without this patch, the following race conditions are possible.
> >
> > Race condition 1:
> > * clk-A has two parents - clk-X and clk-Y.
> > * All three are disabled and clk-X is current parent.
> > * Thread A: clk_set_parent(clk-A, clk-Y).
> > * Thread A:<snip execution flow>
> > * Thread A: Grabs enable lock.
> > * Thread A: Sees enable count of clk-A is 0, so doesn't enable clk-Y.
> > * Thread A: Releases enable lock.
> > * Thread B: Calls clk_enable(clk-A), which in turn enables clk-X.
> > * Thread A: Switches clk-A's parent to clk-Y in hardware.
> >
> > clk-A is now enabled in software, but not clocking in hardware.
> >
> > Race condition 2:
> > * clk-A has two parents - clk-X and clk-Y.
> > * All three are disabled and clk-X is current parent.
> > * Thread A: clk_set_parent(clk-A, clk-Y).
> > * Thread A:<snip execution flow>
> > * Thread A: Switches parent in hardware to clk-Y.
> > * Thread A: Grabs enable lock.
> > * Thread A: Sees enable count of clk-A is 0, so doesn't disable clk-X.
> > * Thread A: Releases enable lock.
> > * Thread B: Calls clk_enable(clk-A)
> > * Thread B: Software state still says parent is clk-X.
> > * Thread B: So, enables clk-X and then itself.
> > * Thread A: Updates parent in software state to clk-Y.
> >
This looks correct to me. Is there any usecase where enabling/disabling a
clock would require sleeping but changing the parent would not?
Cheers,
Peter.
next prev parent reply other threads:[~2012-05-22 13:58 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-12 4:59 [PATCH] clk: Fix race conditions between clk_set_parent() and clk_enable() Saravana Kannan
2012-05-15 18:20 ` Saravana Kannan
2012-05-22 13:58 ` Peter De Schrijver [this message]
2012-05-22 18:06 ` Turquette, Mike
2012-05-23 9:16 ` Peter De Schrijver
2012-05-31 3:46 ` Saravana Kannan
2012-05-15 19:42 ` Sascha Hauer
2012-05-15 19:51 ` Saravana Kannan
2012-05-15 20:00 ` Sascha Hauer
2012-05-15 20:09 ` Saravana Kannan
2012-05-16 5:59 ` Turquette, Mike
2012-05-16 9:19 ` skannan at codeaurora.org
2012-05-15 20:43 ` [PATCH] clk: Fix CLK_SET_RATE_GATE flag validation in clk_set_rate() Saravana Kannan
2012-05-15 22:31 ` Richard Zhao
2012-05-16 0:25 ` Richard Zhao
2012-05-16 5:40 ` Turquette, Mike
2012-05-16 6:00 ` [PATCH] clk: Fix race conditions between clk_set_parent() and clk_enable() Turquette, Mike
2012-05-16 7:30 ` Linus Walleij
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