Re: [PATCH 2/2] scsi: ufs: Fix a deadlock in the error handler

[Christoph Hellwig <hch@infradead.org>]

On Tue, Nov 02, 2021 at 05:05:29PM -0700, Bart Van Assche wrote:
> -	req = blk_get_request(q, REQ_OP_DRV_OUT, 0);
> +	req = blk_mq_alloc_request(q, REQ_OP_DRV_OUT, BLK_MQ_REQ_RESERVED);

blk_get_request will be gone in 5.16-rc, so this won't apply.

But more importantly: SCSI LLDDs have absolutel no business calling
blk_get_request or blk_mq_alloc_request directly, but as usual UFS is
completely fucked up here.

Please add a SCSI midlayer helper to allocate the reserved tags, and
switch _all_ of this UFS we're sending our own commands crap to it
so it doesn't mix with the actual SCSI requests.  We might or might not
want a separate request_queue for them as well as non-SCSI requests
really should not show up in ->queuecommand.  Hannes and John have been
looking into this for a while and we need to sort this out properly.