linux-kernel - Re: block: flush queued bios when the process blocks

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Message-ID: <20151006185016.GA31955@redhat.com>
Date:	Tue, 6 Oct 2015 14:50:16 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, Kent Overstreet <kmo@...erainc.com>,
	dm-devel@...hat.com, linux-kernel@...r.kernel.org,
	"Alasdair G. Kergon" <agk@...hat.com>
Subject: Re: block: flush queued bios when the process blocks

On Tue, Oct 06 2015 at  2:17pm -0400,
Mikulas Patocka <mpatocka@...hat.com> wrote:

> 
> 
> On Mon, 5 Oct 2015, Mike Snitzer wrote:
> 
> > FYI, I've put rebased versions of your 2 patches in my wip branch, see:
> > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/log/?h=wip
> 
> I found a bug in the first patch 
> (http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=2e90df2e9cf482f45be4230152535fdab525fbd8)
> 
> There is this piece of code:
> 
> 	spin_lock(&bs->rescue_lock);
> 	bio_list_add(&bs->rescue_list, bio);
> 	spin_unlock(&bs->rescue_lock);
> 	queue_work(bs->rescue_workqueue, &bs->rescue_work);
> 
> It is possible that after spin_unlock and before queue_work the bio is 
> finished by previous workqueue invocation. When the bio is finished, it is 
> possible that the block device is unloaded and queue_work accesses freed 
> memory.
> 
> Change the code so that queue_work is executed inside the spinlock:
> 	spin_lock(&bs->rescue_lock);
> 	bio_list_add(&bs->rescue_list, bio);
> 	queue_work(bs->rescue_workqueue, &bs->rescue_work);
> 	spin_unlock(&bs->rescue_lock);

OK, but that should get pulled out to a separate stable@ fix that patch
you reference builds on.

I've adjusted my 'wip' branch accordingly (with placeholder commit that
needs revised header, etc).
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