Messages in this thread | | | Date | Mon, 4 May 2015 16:35:51 +0800 | From | Dong Aisheng <> | Subject | Re: [PATCH RFC v1 2/5] clk: add missing lock when call clk_core_enable in clk_set_parent |
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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@linaro.org> > > Cc: Stephen Boyd <sboyd@codeaurora.org> > > Signed-off-by: Dong Aisheng <aisheng.dong@freescale.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
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