lkml.org 
[lkml]   [2022]   [Apr]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH] percpu_ref: call wake_up_all() after percpu_ref_put() completes
    From


    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:

    /* The value of &ref is unstable! */
    percpu_ref_is_zero(&ref)
    (B)percpu_ref_put(ref);

    Thanks,
    Qi

    >

    --
    Thanks,
    Qi

    \
     
     \ /
      Last update: 2022-04-08 06:17    [W:7.838 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site