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

[Bart Van Assche <bvanassche@acm.org>]

On 11/3/21 9:27 AM, Christoph Hellwig wrote:
> On Wed, Nov 03, 2021 at 06:45:34AM -0700, Bart Van Assche wrote:
>>> 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.
> 
> The problem is not the shared tag space, the problem is that it is
> poking through layers.  IFF we have good use cases for just allocating
> a tag (and we don't want to reserve it, which does make sense for many
> things like task management) we need a SCSI layer API that returns just
> the tag (and preferably also poisons the request in some way).

How about changing the blk_mq_alloc_request() / blk_put_request() calls in
ufshcd_exec_dev_cmd() and __ufshcd_issue_tm_cmd() into
scsi_{get,put}_internal_command() calls once Hannes' patch series that
introduces these functions is upstream? See also "[PATCH 03/18] scsi: add
scsi_{get,put}_internal_cmd() helper"
(https://lore.kernel.org/linux-scsi/20210503150333.130310-4-hare@suse.de/).
See also patch "[PATCH 10/18] scsi: implement reserved command handling"
(https://lore.kernel.org/linux-scsi/20210503150333.130310-11-hare@suse.de/).

Thanks,

Bart.