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

From: Bart Van Assche <bvanassche@acm.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: "Martin K . Petersen" <martin.petersen@oracle.com>,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	linux-scsi@vger.kernel.org,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	Can Guo <cang@codeaurora.org>, Bean Huo <beanhuo@micron.com>,
	Stanley Chu <stanley.chu@mediatek.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Asutosh Das <asutoshd@codeaurora.org>,
	Hannes Reinecke <hare@suse.com>,
	John Garry <john.garry@huawei.com>
Subject: Re: [PATCH 2/2] scsi: ufs: Fix a deadlock in the error handler
Date: Wed, 3 Nov 2021 06:45:34 -0700	[thread overview]
Message-ID: <700f0463-23a9-8465-f712-1188cb884dea@acm.org> (raw)
In-Reply-To: <YYI9BLBhrFbgridf@infradead.org>

On 11/3/21 00:40, Christoph Hellwig wrote:
> 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.

Thanks for the reminder Christoph. This is something I am aware of. 
Hence the promise in the cover letter to rebase and repost this patch 
series after the merge window has closed.

> 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.

As explained by Adrian, the UFS protocol uses a single tag space for 
SCSI commands and UFS device commands. blk_mq_alloc_request() is used in 
this context to allocate a tag only from the shared tag space only. I 
think using blk_mq_alloc_request() for that purpose is fine.

Thanks,

Bart.