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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 22 Aug 2020 09:30:25 -0700
Message-ID: <CAADWXX-wpVR5Y1Z=BH5QnMjbsGbkQT__r4D2zCFFVycMDELxOQ@mail.gmail.com>
Subject: Re: [RFC PATCH] pipe: make pipe_release() deferrable.
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        Andrea Arcangeli <aarcange@redhat.com>,
        syzbot <syzbot+96cc7aba7e969b1d305c@syzkaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
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On Fri, Aug 21, 2020 at 9:35 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> Therefore, this patch tries to convert __pipe_lock() in pipe_release() to
> killable, by deferring to a workqueue context when __pipe_lock_killable()
> failed.

I don't think this is an improvement.

If somebody can delay the pipe unlock arbitrarily, you've now turned a
user-visible blocking operation into blocking a workqueue instead. So
it's still there, and now it possibly is much worse and blocks
system_wq instead.

                Linus