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@xxxxxxxxxxxxx> wrote:
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
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
