Re: [PATCH] scsi: ufs: Fix proper API to send HPB pre-request

[Bart Van Assche]

On 10/28/21 7:28 AM, James Bottomley wrote:
> If the block people are happy with this, then I'm OK with it, but it
> doesn't look like you've solved the fanout deadlock problem because
> this new mechanism is still going to allocate a new tag.

(+Jens, Christoph and linux-block)

Hi James,

My understanding is that the UFS HPB code makes ufshcd_queuecommand()
return SCSI_MLQUEUE_HOST_BUSY if the pool with pre-allocated requests is
exhausted. This will make the SCSI core reissue a SCSI command until
completion of another command has freed up one of the pre-allocated
requests. This is not the most efficient approach but should not trigger
a deadlock.

Thanks,

Bart.