Messages in this thread | | | Date | Fri, 8 Apr 2022 12:16:49 +0800 | Subject | Re: [PATCH] percpu_ref: call wake_up_all() after percpu_ref_put() completes | From | Qi Zheng <> |
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On 2022/4/8 12:14 PM, Qi Zheng wrote: > > > On 2022/4/8 12:10 PM, Andrew Morton wrote: >> On Fri, 8 Apr 2022 12:06:20 +0800 Qi Zheng >> <zhengqi.arch@bytedance.com> wrote: >> >>> >>> >>>>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> >>>>>> >>>>>> Are any users affected by this? If so, I think a Fixes tag >>>>>> is necessary. >>>>> >>>>> Looks all current users(blk_pre_runtime_suspend() and >>>>> set_in_sync()) are >>>>> affected by this. >>>>> >>>>> I see that this patch has been merged into the mm tree, can Andrew >>>>> help >>>>> me add the following Fixes tag? >>>> >>>> Andrew is helpful ;) >>>> >>>> Do you see reasons why we should backport this into -stable trees? >>>> It's 8 years old, so my uninformed guess is "no"? >>> >>> Hmm, although the commit 490c79a65708 add wake_up_all(), it is no >>> problem for the usage at that time, maybe the correct Fixes tag is the >>> following: >>> >>> Fixes: 210f7cdcf088 ("percpu-refcount: support synchronous switch to >>> atomic mode.") >>> >>> But in fact, there is no problem with it, but all current users expect >>> the refcount is stable after percpu_ref_switch_to_atomic_sync() returns. >>> >>> I have no idea as which Fixes tag to add. >> >> Well the solution to that problem is to add cc:stable and let Greg >> figure it out ;) >> >> The more serious question is "should we backport this". What is the >> end-user-visible impact of the bug? Do our users need the fix or not? > > The impact on the current user is that it is possible to miss an > opportunity to reach 0 due to the case B in the commit message:
There may be performance issues, but should not cause serious bugs.
> > /* The value of &ref is unstable! */ > percpu_ref_is_zero(&ref) > (B)percpu_ref_put(ref); > > Thanks, > Qi > >> >
-- Thanks, Qi
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