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Date:   Wed, 15 Feb 2023 22:09:36 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Uday Shankar <ushankar@purestorage.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>, linux-block@vger.kernel.org,
        dm-devel@redhat.com
Subject: Re: [PATCH] blk-mq: enforce op-specific segment limits in
 blk_insert_cloned_request
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References: <20230215201507.494152-1-ushankar@purestorage.com>
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On Wed, Feb 15, 2023 at 01:15:08PM -0700, Uday Shankar wrote:
> The block layer might merge together discard requests up until the
> max_discard_segments limit is hit, but blk_insert_cloned_request checks
> the segment count against max_segments regardless of the req op. This
> can result in errors like the following when discards are issued through
> a DM device and max_discard_segments exceeds max_segments for the queue
> of the chosen underlying device.
> 
> blk_insert_cloned_request: over max segments limit. (256 > 129)
> 
> Fix this by looking at the req_op and enforcing the appropriate segment
> limit - max_discard_segments for REQ_OP_DISCARDs and max_segments for
> everything else.

I'd just remove the debug check entirely.