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From: Can Guo <cang@codeaurora.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: asutoshd@codeaurora.org, nguyenb@codeaurora.org,
	hongwus@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 v2 5/6] scsi: ufs: Let host_sem cover the entire system suspend/resume
Date: Tue, 25 May 2021 10:04:23 +0800	[thread overview]
Message-ID: <423285a089b7dc3fcfcb169e0a553e8a@codeaurora.org> (raw)
In-Reply-To: <19b44731-1a4f-c88c-58fd-05eca5df2c2e@acm.org>

Hi Bart,

On 2021-05-25 00:56, Bart Van Assche wrote:
> On 5/24/21 1:47 AM, Can Guo wrote:
>> UFS error handling now is doing more than just re-probing, but also 
>> sending
>> scsi cmds, e.g., for clearing UACs, and recovering runtime PM error, 
>> which
>> may change runtime status of scsi devices. To protect system 
>> suspend/resume
>> from being disturbed by error handling, move the host_sem from wl pm 
>> ops
>> to ufshcd_suspend_prepare() and ufshcd_resume_complete().
> 
> Other SCSI LLDs can perform error handling while system suspend/resume
> is in progress. Why can't the UFS driver do this?

I don't know about other SCSI LLDs, but UFS error handling is basically
doing a re-probe/re-initialization to UFS device. Having UFS error 
handling
running in parallel with system suspend/resume, neither of them will end
up well.

I didn't design all this, it is just happening, I am trying to fix it 
and
semaphore works well for me. I am really glad to see someone cares about
error handling and fix it with better ideas (maybe using WQ_FREEZABLE) 
later.

> 
> Additionally, please document what the purpose of host_sem is before
> making any changes to how host_sem is used. The only documentation I
> have found of host_sem is the following: "* @host_sem: semaphore used 
> to
> serialize concurrent contexts". To me that text is less than useful
> since semaphores are almost always used to serialize concurrent code.
> 

Sure, host_sem is actually preventing cocurrency happens among any of
contexts, such as sysfs access, shutdown, error handling, system
suspend/resume and async probe, I will update its message in next 
version.

Thanks,

Can Guo.

> Thanks,
> 
> Bart.

  reply	other threads:[~2021-05-25  2:04 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-24  8:47 [PATCH v2 0/6] Complementary changes for error handling Can Guo
2021-05-24  8:47 ` [PATCH v2 1/6] scsi: ufs: Differentiate status between hba pm ops and wl pm ops Can Guo
2021-05-24  8:47 ` [PATCH v2 2/6] scsi: ufs: Update the return value of supplier " Can Guo
2021-05-24  8:47 ` [PATCH v2 3/6] scsi: ufs: Simplify error handling preparation Can Guo
2021-05-24  8:47 ` [PATCH v2 4/6] scsi: ufs: Update ufshcd_recover_pm_error() Can Guo
2021-05-24  8:47 ` [PATCH v2 5/6] scsi: ufs: Let host_sem cover the entire system suspend/resume Can Guo
2021-05-24 16:56   ` Bart Van Assche
2021-05-25  2:04     ` Can Guo [this message]
2021-05-24  8:47 ` [PATCH v2 6/6] scsi: ufs: Update the fast abort path in ufshcd_abort() for PM requests Can Guo

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