Messages in this thread | | | Date | Wed, 6 May 2015 17:01:54 -0700 | From | Stephen Boyd <> | 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 05/04, Dong Aisheng wrote: > 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? >
Ah I see now. The commit text could say something like this:
Before commit 035a61c314eb ("clk: Make clk API return per-user struct clk instances") we acquired the enable_lock in __clk_set_parent_{before,after}() by means of calling clk_enable(). After commit 035a61c314eb we use clk_core_enable() in place of the clk_enable(), and clk_core_enable() doesn't acquire the enable_lock. This opens up a race condition between clk_set_parent() and clk_enable().
I've replaced the commit text and applied it to clk-fixes.
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