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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 13 Jun 2018 07:06:44 -0700
Message-ID: <CA+55aFz0tL4c5wrCcjukph95qQ+97Dmxpq4Ct7raqkiEJX-8xQ@mail.gmail.com>
Subject: Re: [PATCH] bdi: Fix another oops in wb_workfn()
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Jens Axboe <axboe@kernel.dk>,
        syzbot+4a7438e774b21ddd8eca@syzkaller.appspotmail.com,
        syzkaller-bugs@googlegroups.com,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Dave Chinner <david@fromorbit.com>,
        linux-block <linux-block@vger.kernel.org>
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On Wed, Jun 13, 2018 at 3:44 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> Can't we utilize RCU grace period (like shown below) ?

_Please_ don't do conditional locking. Particularly not the kind where
then a function drops the lock that was taken in another function -
and only does it based on some parameter.

Yes, we have cases where we do it, but it's seldom a great idea, and
it _really_ makes for subtle code (and subtle bugs).

                  Linus