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Date: Mon, 4 May 2015 16:35:51 +0800 From: Dong Aisheng <b29396@...escale.com> To: Stephen Boyd <sboyd@...eaurora.org> CC: Dong Aisheng <aisheng.dong@...escale.com>, <linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <mturquette@...aro.org>, <shawn.guo@...aro.org>, <linux-arm-kernel@...ts.infradead.org>, <Ranjani.Vaidyanathan@...escale.com>, <b20596@...escale.com>, <r64343@...escale.com>, <b20788@...escale.com> Subject: Re: [PATCH RFC v1 2/5] clk: add missing lock when call clk_core_enable in clk_set_parent On Thu, Apr 30, 2015 at 12:07:47PM -0700, Stephen Boyd wrote: > On 04/15/15 07:26, Dong Aisheng wrote: > > clk_core_enable is executed without &enable_clock in clk_set_parent function. > > Adding it to avoid potential race condition issue. > > > > Fixes: 035a61c314eb ("clk: Make clk API return per-user struct clk instances") > > Cc: Mike Turquette <mturquette@...aro.org> > > Cc: Stephen Boyd <sboyd@...eaurora.org> > > Signed-off-by: Dong Aisheng <aisheng.dong@...escale.com> > > --- > > Can you please describe the race condition? From what I can tell there > is not a race condition here and we've gone around on this part of the > code before to fix any race conditions. > Do you mean we do not need to acquire enable lock when execute clk_core_enable in set_parent function? Can you help explain a bit more why? The clk doc looks to me says the enable lock should be held across calls to the .enable, .disable and .is_enabled operations. And before the commit 035a61c314eb ("clk: Make clk API return per-user struct clk instances"), all the clk_enable/disable in set_parent() is executed with lock. A rough thinking of race condition is assuming Thread A calls clk_set_parent(x, y) while Thread B calls clk_enable(x), clock x is disabled but prepared initially, due to clk_core_enable in set_parent() is not executed with enable clock, the clk_core_enable may be reentrant during the locking time executed by B. Won't this be a race condition? Regards Dong Aisheng > -- > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > a Linux Foundation Collaborative Project > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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