From: Adrian Hunter <adrian.hunter@intel.com>
To: Can Guo <cang@codeaurora.org>
Cc: 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: Wed, 7 Jul 2021 22:04:06 +0300 [thread overview]
Message-ID: <bd464b9f-b6d5-cd52-7377-c64c0cf933ff@intel.com> (raw)
In-Reply-To: <7c6e2baa3578eb30f2d4bd1696e800eb@codeaurora.org>
On 28/06/21 10:26 am, Can Guo wrote:
> On 2021-06-24 18:04, Adrian Hunter wrote:
>> On 24/06/21 9:31 am, Can Guo wrote:
>>> On 2021-06-24 14:23, Adrian Hunter wrote:
>>>> On 24/06/21 9:12 am, Can Guo wrote:
>>>>> On 2021-06-24 13:52, Adrian Hunter wrote:
>>>>>> On 24/06/21 5:16 am, Can Guo wrote:
>>>>>>> On 2021-06-23 22:30, Adrian Hunter wrote:
>>>>>>>> On 23/06/21 10:35 am, Can Guo wrote:
>>>>>>>>> To protect system suspend/resume from being disturbed by error handling,
>>>>>>>>> instead of using host_sem, let error handler call lock_system_sleep() and
>>>>>>>>> unlock_system_sleep() which achieve the same purpose. Remove the host_sem
>>>>>>>>> used in suspend/resume paths to make the code more readable.
>>>>>>>>>
>>>>>>>>> Suggested-by: Bart Van Assche <bvanassche@acm.org>
>>>>>>>>> Signed-off-by: Can Guo <cang@codeaurora.org>
>>>>>>>>> ---
>>>>>>>>> drivers/scsi/ufs/ufshcd.c | 12 +++++++-----
>>>>>>>>> 1 file changed, 7 insertions(+), 5 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>>>>>>>>> index 3695dd2..a09e4a2 100644
>>>>>>>>> --- a/drivers/scsi/ufs/ufshcd.c
>>>>>>>>> +++ b/drivers/scsi/ufs/ufshcd.c
>>>>>>>>> @@ -5907,6 +5907,11 @@ static void ufshcd_clk_scaling_suspend(struct ufs_hba *hba, bool suspend)
>>>>>>>>>
>>>>>>>>> static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
>>>>>>>>> {
>>>>>>>>> + /*
>>>>>>>>> + * It is not safe to perform error handling while suspend or resume is
>>>>>>>>> + * in progress. Hence the lock_system_sleep() call.
>>>>>>>>> + */
>>>>>>>>> + lock_system_sleep();
>>>>>>>>
>>>>>>>> It looks to me like the system takes this lock quite early, even before
>>>>>>>> freezing tasks, so if anything needs the error handler to run it will
>>>>>>>> deadlock.
>>>>>>>
>>>>>>> Hi Adrian,
>>>>>>>
>>>>>>> UFS/hba system suspend/resume does not invoke or call error handling in a
>>>>>>> synchronous way. So, whatever UFS errors (which schedules the error handler)
>>>>>>> happens during suspend/resume, error handler will just wait here till system
>>>>>>> suspend/resume release the lock. Hence no worries of deadlock here.
>>>>>>
>>>>>> It looks to me like the state can change to UFSHCD_STATE_EH_SCHEDULED_FATAL
>>>>>> and since user processes are not frozen, nor file systems sync'ed, everything
>>>>>> is going to deadlock.
>>>>>> i.e.
>>>>>> I/O is blocked waiting on error handling
>>>>>> error handling is blocked waiting on lock_system_sleep()
>>>>>> suspend is blocked waiting on I/O
>>>>>>
>>>>>
>>>>> Hi Adrian,
>>>>>
>>>>> First of all, enter_state(suspend_state_t state) uses mutex_trylock(&system_transition_mutex).
>>>>
>>>> Yes, in the case I am outlining it gets the mutex.
>>>>
>>>>> Second, even that happens, in ufshcd_queuecommand(), below logic will break the cycle, by
>>>>> fast failing the PM request (below codes are from the code tip with this whole series applied).
>>>>
>>>> It won't get that far because the suspend will be waiting to sync filesystems.
>>>> Filesystems will be waiting on I/O.
>>>> I/O will be waiting on the error handler.
>>>> The error handler will be waiting on system_transition_mutex.
>>>> But system_transition_mutex is already held by PM core.
>>>
>>> Hi Adrian,
>>>
>>> You are right.... I missed the action of syncing filesystems...
>>>
>>> Using back host_sem in suspend_prepare()/resume_complete() won't have this
>>> problem of deadlock, right?
>>
>> I am not sure, but what was problem that the V3 patch was fixing?
>> Can you give an example?
>
> V3 was moving host_sem from wl_system_suspend/resume() to
> ufshcd_suspend_prepare()/ufshcd_resume_complete(). It is to
> make sure error handling does not run concurrenly with system
> PM, since error handling is recovering/clearing runtime PM
> errors of all the scsi devices under hba (in patch #8). Having the
> error handling doing so (in patch 8) is because runtime PM framework
> may save the runtime errors of the supplier to one or more consumers (
> unlike the children - parent relationship), for example if wlu resume
> fails, sda and/or other scsi devices may save the resume error, then
> they will be left runtime suspended permanently.
Sorry for the slow reply. I was going to do some more investigation but
never found time.
I was wondering if it would be simpler to do the error recovery for
wl_system_suspend/resume() before exiting wl_system_suspend/resume().
Then it would be possible to do something along the lines:
- prevent runtime suspend while the error handler is outstanding
- at suspend, block queuing of the error handler work and flush it
- at resume, allow queuing of the error handler work
next prev parent reply other threads:[~2021-07-07 19:04 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 [this message]
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
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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