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Date: Thu, 13 Feb 2025 07:32:14 +0100
From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: Cheyenne Wills <cheyenne.wills@gmail.com>, linux-block@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>
Subject: Re: BUG: NULL pointer dereferenced within __blk_rq_map_sg
Message-ID: <20250213063214.GA20171@lst.de>
References: <CAHpsFVeew-p9xB9DB52Pk_6mXfFxJbT8p14h5+YRTKabEfU3BQ@mail.gmail.com> <Z6s-3LndN-Gt5sZB@fedora> <Z6tss9YS98AEIwQy@fedora> <CAHpsFVcMnSJgJbGrqiBDmYkHyneJdby4DMkOKQKAuicA0kgJQA@mail.gmail.com> <Z61LEUdHI2Hx3bue@fedora>
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On Thu, Feb 13, 2025 at 09:29:53AM +0800, Ming Lei wrote:
> Yeah, turns out oops is triggered in initializing req_iterator for
> discard req, and the following patch should be enough:

How do we end up in blk_rq_map_sg for a discard request here?
dma-mapping doesn't make sense for a non-special pyaload discard
as used by xxen-blkfront, and xen-blkfront also only calls
blk_rq_map_sg from blkif_queue_rw_req and not blkif_queue_discard_req.