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From: Adrian Hunter <adrian.hunter@intel.com>
To: Bart Van Assche <bvanassche@acm.org>,
	"Martin K . Petersen" <martin.petersen@oracle.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>,
	linux-scsi@vger.kernel.org,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	Bean Huo <beanhuo@micron.com>, Can Guo <cang@codeaurora.org>,
	Avri Altman <avri.altman@wdc.com>,
	Stanley Chu <stanley.chu@mediatek.com>,
	Asutosh Das <asutoshd@codeaurora.org>
Subject: Re: [PATCH v2 11/20] scsi: ufs: Switch to scsi_(get|put)_internal_cmd()
Date: Tue, 30 Nov 2021 21:15:21 +0200	[thread overview]
Message-ID: <e214da03-ce47-9987-09d9-2bbf125b59bf@intel.com> (raw)
In-Reply-To: <2cb66e0a-df1e-0825-67b9-cbd2f116fe92@acm.org>

On 30/11/2021 19:51, Bart Van Assche wrote:
> On 11/29/21 10:41 PM, Adrian Hunter wrote:
>> On 29/11/2021 21:32, Bart Van Assche wrote:
>>> * The code in blk_cleanup_queue() that waits for pending requests to finish
>>>    before resources associated with the request queue are freed.
>>>    ufshcd_remove() calls blk_cleanup_queue(hba->cmd_queue) and hence waits until
>>>    pending device management commands have finished. That would no longer be the
>>>    case if the block layer is bypassed to submit device management commands.
>>
>> cmd_queue is used only by the UFS driver, so if the driver is racing with
>> itself at "remove", then that should be fixed. The risk is not that the UFS
>> driver might use requests, but that it might still be operating when hba or
>> other resources get freed.
>>
>> So the question remains, for device commands, we do not need the block
>> layer, nor SCSI commands which still begs the question, why involve them
>> at all?
> 
> By using the block layer request allocation functions the block layer guarantees
> that each tag is in use in only one context. When bypassing the block layer code
> would have to be inserted in ufshcd_exec_dev_cmd() and ufshcd_issue_devman_upiu_cmd()
> to serialize these functions.

They already are serialized, but you are essentially saying the functionality
being duplicated is just a lock.  What you are proposing seems awfully
complicated just to get the functionality of a lock.

> In other words, we would be duplicating existing
> functionality if we bypass the block layer. The recommended approach in the Linux
> kernel is not to duplicate existing functionality.

More accurately, the functionality would not be being used at all, so not
really any duplication.



  reply	other threads:[~2021-11-30 19:15 UTC|newest]

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-19 19:57 [PATCH v2 00/20] UFS patches for kernel v5.17 Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 01/20] block: Add a flag for internal commands Bart Van Assche
2021-11-22  8:46   ` John Garry
2021-11-22 17:38     ` Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 02/20] scsi: core: Unexport scsi_track_queue_full() Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 03/20] scsi: core: Fix scsi_device_max_queue_depth() Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 04/20] scsi: core: Fix a race between scsi_done() and scsi_times_out() Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 05/20] scsi: core: Add support for internal commands Bart Van Assche
2021-11-22  8:58   ` John Garry
2021-11-22 17:46     ` Bart Van Assche
2021-11-22 18:08       ` John Garry
2021-11-22 19:04       ` Bart Van Assche
2021-11-23  8:13       ` Hannes Reinecke
2021-11-23 17:46         ` Bart Van Assche
2021-11-23 19:18           ` Bart Van Assche
2021-11-24  6:33             ` Hannes Reinecke
2021-11-19 19:57 ` [PATCH v2 06/20] scsi: core: Add support for reserved tags Bart Van Assche
2021-11-22  8:15   ` John Garry
2021-11-22 17:25     ` Bart Van Assche
2021-11-22 18:13       ` John Garry
2021-11-19 19:57 ` [PATCH v2 07/20] scsi: ufs: Rename a function argument Bart Van Assche
2021-11-22 20:25   ` Bean Huo
2021-11-19 19:57 ` [PATCH v2 08/20] scsi: ufs: Remove is_rpmb_wlun() Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 09/20] scsi: ufs: Remove the sdev_rpmb member Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 10/20] scsi: ufs: Remove dead code Bart Van Assche
2021-11-24 11:11   ` Adrian Hunter
2021-11-29 19:12     ` Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 11/20] scsi: ufs: Switch to scsi_(get|put)_internal_cmd() Bart Van Assche
2021-11-23 12:20   ` Bean Huo
2021-11-23 17:54     ` Bart Van Assche
2021-11-23 19:41     ` Bart Van Assche
2021-11-24 18:18       ` Bean Huo
2021-11-24 11:02   ` Adrian Hunter
2021-11-24 11:15     ` Adrian Hunter
2021-11-29 19:32     ` Bart Van Assche
2021-11-30  6:41       ` Adrian Hunter
2021-11-30 17:51         ` Bart Van Assche
2021-11-30 19:15           ` Adrian Hunter [this message]
2021-11-30 19:21             ` Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 12/20] scsi: ufs: Rework ufshcd_change_queue_depth() Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 13/20] scsi: ufs: Fix a deadlock in the error handler Bart Van Assche
2021-11-30  8:54   ` Bean Huo
2021-11-30 17:52     ` Bart Van Assche
2021-11-30 19:32     ` Bart Van Assche
2021-12-01 13:44       ` Bean Huo
2021-12-01 18:31         ` Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 14/20] scsi: ufs: Introduce ufshcd_release_scsi_cmd() Bart Van Assche
2021-11-24 12:03   ` Adrian Hunter
2021-11-30 18:00     ` Bart Van Assche
2021-11-30 19:02       ` Adrian Hunter
2021-11-30 19:16         ` Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 15/20] scsi: ufs: Improve SCSI abort handling Bart Van Assche
2021-11-24 12:28   ` Adrian Hunter
2021-11-30  4:13     ` Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 16/20] scsi: ufs: Fix a kernel crash during shutdown Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 17/20] scsi: ufs: Stop using the clock scaling lock in the error handler Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 18/20] scsi: ufs: Optimize the command queueing code Bart Van Assche
2021-11-22 17:46   ` Asutosh Das (asd)
2021-11-22 18:13     ` Bart Van Assche
2021-11-22 23:02       ` Asutosh Das (asd)
2021-11-22 23:48         ` Bart Van Assche
2021-11-23 18:24           ` Asutosh Das (asd)
2021-12-01 18:33             ` Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 19/20] scsi: ufs: Implement polling support Bart Van Assche
2021-11-30  8:43   ` Bean Huo
2021-11-30  8:57     ` Avri Altman
2021-11-30  9:15       ` Bean Huo
2021-11-30 14:26     ` Bart Van Assche
2021-11-30 15:40       ` Bean Huo
2021-11-30 17:34         ` Bart Van Assche
2021-11-30 17:37     ` Bart Van Assche
2021-11-19 19:57 ` [PATCH v2 20/20] scsi: ufs: Fix race conditions related to driver data Bart Van Assche

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