From: Can Guo <cang@codeaurora.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>,
asutoshd@codeaurora.org, nguyenb@codeaurora.org,
hongwus@codeaurora.org, ziqichen@codeaurora.org,
linux-scsi@vger.kernel.org, kernel-team@android.com,
Alim Akhtar <alim.akhtar@samsung.com>,
Avri Altman <avri.altman@wdc.com>,
"James E.J. Bottomley" <jejb@linux.ibm.com>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
Stanley Chu <stanley.chu@mediatek.com>,
Bean Huo <beanhuo@micron.com>, Jaegeuk Kim <jaegeuk@kernel.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 06/10] scsi: ufs: Remove host_sem used in suspend/resume
Date: Tue, 29 Jun 2021 14:23:28 +0800 [thread overview]
Message-ID: <60a5496863100976b74d8c376c9e9cb0@codeaurora.org> (raw)
In-Reply-To: <c7d9e12d-f966-44c6-27dc-4004143398aa@acm.org>
On 2021-06-29 01:31, Bart Van Assche wrote:
> On 6/28/21 1:17 AM, Can Guo wrote:
>> On 2021-06-25 01:11, Bart Van Assche wrote:
>>> On 6/23/21 11:31 PM, Can Guo wrote:
>>>> Using back host_sem in suspend_prepare()/resume_complete() won't
>>>> have
>>>> this problem of deadlock, right?
>>>
>>> Although that would solve the deadlock discussed in this email
>>> thread, it
>>> wouldn't solve the issue of potential adverse interactions of the UFS
>>> error handler and the SCSI error handler running concurrently.
>>
>> I think I've explained it before, paste it here -
>>
>> ufshcd_eh_host_reset_handler() invokes ufshcd_err_handler() and
>> flushes it,
>> so SCSI error handler and UFS error handler can safely run together.
>
> That code path is the exception. Do you agree that the following three
> functions all invoke the ufshcd_err_handler() function asynchronously?
> * ufshcd_uic_pwr_ctrl()
> * ufshcd_check_errors()
> * ufshcd_abort()
>
I agree, but I don't see what's wrong with that. Any context can invoke
ufs error handler asynchronously and ufs error handler prepare makes
sure error handler can work safely, i.e., stopping PM ops/gating/scaling
in error handler prepare makes sure no one shall call
ufshcd_uic_pwr_ctrl()
ever again. And ufshcd_check_errors() and ufshcd_abort() are OK to run
concurrently with UFS error handler.
>>> How about using the
>>> standard approach for invoking the UFS error handler instead of using
>>> a custom
>>> mechanism, e.g. by using something like the (untested) patch below?
>>> This
>>> approach guarantees that the UFS error handler is only activated
>>> after
>>> all
>>> pending SCSI commands have failed or timed out and also guarantees
>>> that no new
>>> SCSI commands will be queued while the UFS error handler is in
>>> progress (see
>>> also scsi_host_queue_ready()).
>>
>> Per my understanding, SCSI error handling is scsi cmd based, meaning
>> it
>> only works when certain SCSI cmds failed [ ... ]
> That is not completely correct. The SCSI error handler is activated if
> either all pending commands have failed or if it is scheduled
> explicitly. Please take a look at the host_eh_scheduled member
> variable,
> how it is used and also at scsi_schedule_eh(). The scsi_schedule_eh()
> function was introduced in 2006 and that the ATA code uses it since
> then
> to activate the SCSI error handler even if no commands are pending. See
> also the patch "SCSI: make scsi_implement_eh() generic API for SCSI
> transports".
>
>> However, most UFS (UIC) errors happens during gear scaling, clk gating
>> and suspend/resume (due to power mode changes and/or hibern8
>> enter/exit), during which there is NO scsi cmds in UFS driver at all
>> (because these contexts start only when there is no ongoing data
>> transactions).
>
> Activating the SCSI error handler if no SCSI commands are in progress
> is
> supported by scsi_schedule_eh().
>
>> Thus, scsi_unjam_host() won't even call scsi_eh_ready_devs() because
>> scsi_eh_get_sense() always returns TRUE in these cases (eh_work_q is
>> empty).
>
> Please take another look at the patch in my previous message. There is
> a
> scsi_transport_template instance in that patch. The eh_strategy_handler
> defined in a SCSI transport template is called *instead* of
> scsi_unjam_host(). In other words, scsi_unjam_host() won't be called if
> my patch would be applied to the UFS driver.
>
> Please let me know if you need more information.
Sorry that I missed the change of scsi_transport_template() in your
previous
message. I can understand that you want to invoke UFS error hander by
invoking
SCSI error handler, but I didn't go that far because I saw you changed
pm_runtime_get_sync() to pm_runtime_get_noresume() in ufs error handler
prepare.
How can that change make sure that the device is not suspending or
resuming
while error handler is running?
Thanks,
Can Guo.
>
> Bart.
next prev parent reply other threads:[~2021-06-29 6:23 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1624433711-9339-1-git-send-email-cang@codeaurora.org>
2021-06-23 7:35 ` [PATCH v4 01/10] scsi: ufs: Rename flags pm_op_in_progress and is_sys_suspended Can Guo
2021-06-23 20:05 ` Bart Van Assche
2021-06-23 20:57 ` Bart Van Assche
2021-06-24 2:02 ` Can Guo
2021-06-24 2:34 ` Can Guo
2021-06-24 6:04 ` Adrian Hunter
2021-06-23 20:42 ` Bjorn Andersson
2021-06-23 22:41 ` Bart Van Assche
2021-06-24 2:04 ` Can Guo
2021-06-24 17:32 ` Bart Van Assche
2021-06-24 23:42 ` Bart Van Assche
2021-06-28 7:01 ` Can Guo
2021-06-28 7:35 ` Can Guo
2021-06-28 17:07 ` Bart Van Assche
2021-06-23 7:35 ` [PATCH v4 02/10] scsi: ufs: Add " Can Guo
2021-06-23 12:33 ` Adrian Hunter
2021-06-24 2:05 ` Can Guo
2021-06-23 20:59 ` Bart Van Assche
2021-06-24 2:07 ` Can Guo
2021-06-24 17:35 ` Bart Van Assche
2021-06-28 7:11 ` Can Guo
2021-06-23 7:35 ` [PATCH v4 03/10] scsi: ufs: Update the return value of supplier pm ops Can Guo
2021-06-23 21:08 ` Bart Van Assche
2021-06-24 2:11 ` Can Guo
2021-06-23 7:35 ` [PATCH v4 04/10] scsi: ufs: Enable IRQ after enabling clocks in error handling preparation Can Guo
2021-06-23 21:20 ` Bart Van Assche
2021-06-23 7:35 ` [PATCH 05/10] scsi: ufs: Complete the cmd before returning in queuecommand Can Guo
2021-06-23 7:39 ` Can Guo
2021-06-23 7:35 ` [PATCH v4 05/10] scsi: ufs: Remove a redundant tag check in ufshcd_queuecommand() Can Guo
2021-06-23 21:24 ` Bart Van Assche
2021-06-23 7:35 ` [PATCH v4 06/10] scsi: ufs: Remove host_sem used in suspend/resume Can Guo
2021-06-23 14:30 ` Adrian Hunter
2021-06-24 2:16 ` Can Guo
2021-06-24 5:52 ` Adrian Hunter
2021-06-24 6:12 ` Can Guo
2021-06-24 6:23 ` Adrian Hunter
2021-06-24 6:31 ` Can Guo
2021-06-24 10:04 ` Adrian Hunter
2021-06-28 7:26 ` Can Guo
2021-07-07 19:04 ` Adrian Hunter
2021-06-24 17:11 ` Bart Van Assche
2021-06-28 8:17 ` Can Guo
2021-06-28 17:31 ` Bart Van Assche
2021-06-29 6:23 ` Can Guo [this message]
2021-06-29 18:01 ` Bart Van Assche
2021-06-29 21:50 ` Can Guo
2021-06-23 7:35 ` [PATCH v4 07/10] scsi: ufs: Simplify error handling preparation Can Guo
2021-06-23 21:30 ` Bart Van Assche
2021-06-23 7:35 ` [PATCH v4 08/10] scsi: ufs: Update ufshcd_recover_pm_error() Can Guo
2021-06-23 7:35 ` [PATCH v4 09/10] scsi: ufs: Update the fast abort path in ufshcd_abort() for PM requests Can Guo
2021-06-23 21:33 ` Bart Van Assche
2021-06-24 4:16 ` Can Guo
2021-06-24 16:57 ` Bart Van Assche
2021-06-23 7:35 ` [PATCH v4 10/10] scsi: ufs: Apply more limitations to user access Can Guo
2021-06-23 21:51 ` Bart Van Assche
2021-06-24 2:23 ` Can Guo
2021-06-24 22:25 ` Bart Van Assche
2021-06-28 7:16 ` Can Guo
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