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Date:   Tue, 18 Apr 2023 06:57:19 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Mikulas Patocka <mpatocka@redhat.com>,
        Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Mike Snitzer <msnitzer@redhat.com>, dm-devel@redhat.com,
        linux-block@vger.kernel.org
Subject: Re: [PATCH] block: fix a crash when bio_for_each_folio_all
 iterates over an empty bio
Message-ID: <20230418045719.GA29490@lst.de>
References: <alpine.LRH.2.21.2304171433370.17217@file01.intranet.prod.int.rdu2.redhat.com> <ZD2e5lw5CqueygSA@casper.infradead.org>
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On Mon, Apr 17, 2023 at 08:32:54PM +0100, Matthew Wilcox wrote:
> On Mon, Apr 17, 2023 at 03:11:57PM -0400, Mikulas Patocka wrote:
> > If we use bio_for_each_folio_all on an empty bio, it will access the first
> > bio vector unconditionally (it is uninitialized) and it may crash
> > depending on the uninitialized data.
> 
> Wait, how do we have an empty bio in the first place?

flush bios are always empty.  Not sure iterating over them makes much
sense, though.