linux-kernel - Re: bcache: oops when writing to writeback

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Date:   Wed, 5 Jun 2019 11:21:46 +0200
From:   Bjørn Forsman <bjorn.forsman@...il.com>
To:     Coly Li <colyli@...e.de>
Cc:     Kent Overstreet <kent.overstreet@...il.com>,
        linux-bcache@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: bcache: oops when writing to writeback_percent without a cache device

On Wed, 5 Jun 2019 at 06:41, Coly Li <colyli@...e.de> wrote:
>
> On 2019/6/5 1:24 上午, Bjørn Forsman wrote:
> > On Tue, 4 Jun 2019 at 17:41, Coly Li <colyli@...e.de> wrote:
> >>
> >> On 2019/6/4 10:59 下午, Coly Li wrote:
> >>> On 2019/6/4 7:00 下午, Bjørn Forsman wrote:
> >>>> Hi all,
> >>>>
> >>>> I get a kernel oops from bcache when writing to
> >>>> /sys/block/bcache0/bcache/writeback_percent and there is no attached
> >>>> cache device. See the oops itself below my signature.
> >>>>
> >>>> This is on Linux 4.19.46. I looked in git and see many commits to
> >>>> bcache lately, but none seem to address this particular issue.
> >>>>
> >>>> Background: I'm writing to .../writeback_percent with
> >>>> systemd-tmpfiles. I'd rather not replace it with a script that figures
> >>>> out whether or not the kernel will oops if writing to the sysfs file
> >>>> -- the kernel should not oops in the first place.
> >>>
> >>> Hi Bjorn,
> >>>
> >>> Thank you for the reporting. I believe this is a case we missed in
> >>> testings. When a bcache device is not attached, it does not make sense
> >>> to update the writeback rate in period by the changing of writeback_percent.
> >>>
> >>> I will post a patch for your testing soon.
> >>
> >> Hi Bjorn,
> >>
> >> Could you please to try this patch ? Hope it may help a bit.
> >
> > Hi Coly,
> >
> > Thanks for the quick patch! I tested it on linux 5.2-rc2 and it indeed
> > fixes the problem.
> >
> > There is one typo in the patch/commit message: s/writebac/writeback/
> >
>
> Hi Bjorn,
>
> Thanks for the patch review. Do you mind if I add Reviewed-By: tag with
> your name and email address ?

Yes, you can add my Reviewed-By: tag.

-- 
Bjørn Forsman