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

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Date:   Wed, 13 Jun 2018 07:55:32 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jan Kara <jack@...e.cz>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        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 7:46 AM Jan Kara <jack@...e.cz> wrote:
>
> On Wed 13-06-18 19:43:47, Tetsuo Handa wrote:
> > Can't we utilize RCU grace period (like shown below) ?
>
> Honestly, the variant 1 looks too ugly to me. However variant 2 looks
> mostly OK.

The versions that don't have that conditional locking look fine to me, yes.

> Also I'd avoid the addition argument to wb_writeback() and split the function instead. The
> patch resulting from your and mine ideas is attached. Thoughts?

Is there a reason for this model:

+               if (cgwb_start_shutdown(wb))
+                       __wb_shutdown(wb);

when there is just one call site of this? Why not just make the
function void, and make it do that __wb_shutdown() itself in the true
case?

IOW, just make it be

+               cgwb_shutdown(wb);

instead?

That's what "wb_shutdown()" does - it does the "wb_start_shutdown()"
test internally, and does __wb_shutdown() all inside itself, instead
of expecting the caller to do it.

I dunno.

              Linus

              Linus