| Message ID | 1429107999-24413-3-git-send-email-aisheng.dong@freescale.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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.
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 > -- > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > a Linux Foundation Collaborative Project >
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.
On Wed, May 06, 2015 at 05:01:54PM -0700, Stephen Boyd wrote: > 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. > Got it. Thanks for the change. Regards Dong Aisheng > -- > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > a Linux Foundation Collaborative Project
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index cc56ba2..492644f 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -1475,8 +1475,10 @@ static struct clk_core *__clk_set_parent_before(struct clk_core *clk, */ if (clk->prepare_count) { clk_core_prepare(parent); + flags = clk_enable_lock(); clk_core_enable(parent); clk_core_enable(clk); + clk_enable_unlock(flags); } /* update the clk tree topology */ @@ -1491,13 +1493,17 @@ static void __clk_set_parent_after(struct clk_core *clk, struct clk_core *parent, struct clk_core *old_parent) { + unsigned long flags; + /* * Finish the migration of prepare state and undo the changes done * for preventing a race with clk_enable(). */ if (clk->prepare_count) { + flags = clk_enable_lock(); clk_core_disable(clk); clk_core_disable(old_parent); + clk_enable_unlock(flags); clk_core_unprepare(old_parent); } } @@ -1525,8 +1531,10 @@ static int __clk_set_parent(struct clk_core *clk, struct clk_core *parent, clk_enable_unlock(flags); if (clk->prepare_count) { + flags = clk_enable_lock(); clk_core_disable(clk); clk_core_disable(parent); + clk_enable_unlock(flags); clk_core_unprepare(parent); } return ret;
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> --- drivers/clk/clk.c | 8 ++++++++ 1 file changed, 8 insertions(+)