linux-kernel - Re: [PATCH] bdi: Fix another oops in wb

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Message-ID: <CA+55aFz0tL4c5wrCcjukph95qQ+97Dmxpq4Ct7raqkiEJX-8xQ@mail.gmail.com>
Date:   Wed, 13 Jun 2018 07:06:44 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jens Axboe <axboe@...nel.dk>,
        syzbot+4a7438e774b21ddd8eca@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dave Chinner <david@...morbit.com>,
        linux-block <linux-block@...r.kernel.org>
Subject: Re: [PATCH] bdi: Fix another oops in wb_workfn()

On Wed, Jun 13, 2018 at 3:44 AM Tetsuo Handa
<penguin-kernel@...ove.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