linux-scsi.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Stanley Chu <stanley.chu@mediatek.com>
To: Can Guo <cang@codeaurora.org>
Cc: "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
	"avri.altman@wdc.com" <avri.altman@wdc.com>,
	"alim.akhtar@samsung.com" <alim.akhtar@samsung.com>,
	"jejb@linux.ibm.com" <jejb@linux.ibm.com>,
	"bvanassche@acm.org" <bvanassche@acm.org>,
	"beanhuo@micron.com" <beanhuo@micron.com>,
	"asutoshd@codeaurora.org" <asutoshd@codeaurora.org>,
	"matthias.bgg@gmail.com" <matthias.bgg@gmail.com>,
	"linux-mediatek@lists.infradead.org"
	<linux-mediatek@lists.infradead.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Kuohong Wang (王國鴻)" <kuohong.wang@mediatek.com>,
	"Peter Wang (王信友)" <peter.wang@mediatek.com>,
	"Chun-Hung Wu (巫駿宏)" <Chun-hung.Wu@mediatek.com>,
	"Andy Teng ( ^[$B{}G!9(^[(B)" <Andy.Teng@mediatek.com>,
	"Chaotian Jing (井朝天)" <Chaotian.Jing@mediatek.com>,
	"CC Chou (周志杰)" <cc.chou@mediatek.com>
Subject: Re: [PATCH v4] scsi: ufs: Quiesce all scsi devices before shutdown
Date: Fri, 31 Jul 2020 16:22:53 +0800	[thread overview]
Message-ID: <1596183773.17247.60.camel@mtkswgap22> (raw)
In-Reply-To: <84510fc12ada0de8284e6a689b7a2358@codeaurora.org>

Hi Can,

On Mon, 2020-07-27 at 15:30 +0800, Can Guo wrote:
> Hi Stanley,
> 
> On 2020-07-24 22:01, Stanley Chu wrote:
> > Currently I/O request could be still submitted to UFS device while
> > UFS is working on shutdown flow. This may lead to racing as below
> > scenarios and finally system may crash due to unclocked register
> > accesses.
> > 
> > To fix this kind of issues, specifically quiesce all SCSI devices
> > before UFS shutdown to block all I/O request sending from block
> > layer.
> > 
> > Example of racing scenario: While UFS device is runtime-suspended
> > 
> > Thread #1: Executing UFS shutdown flow, e.g.,
> >            ufshcd_suspend(UFS_SHUTDOWN_PM)
> > Thread #2: Executing runtime resume flow triggered by I/O request,
> >            e.g., ufshcd_resume(UFS_RUNTIME_PM)
> > 
> 
> I don't quite get it, how can you prevent block layer PM from iniating
> hba runtime resume by quiescing the scsi devices? Block layer PM
> iniates hba async runtime resume in blk_queue_enter(). But quiescing
> the scsi devices can only prevent general I/O requests from passing
> through scsi_queue_rq() callback.
> 
> Say hba is runtime suspended, if an I/O request to sda is sent from
> block layer (sda must be runtime suspended as well at this time),
> blk_queue_enter() initiates async runtime resume for sda. But since
> sda's parents are also runtime suspended, the RPM framework shall do
> runtime resume to the devices in the sequence hba->host->target->sda.
> In this case, ufshcd_resume() still runs concurrently, no?
> 

You are right. This patch can not fix the case you mentioned. It just
prevents "general I/O requests".

So perhaps we also need below patch?

#2 scsi: ufs: Use pm_runtime_get_sync in shutdown flow
https://patchwork.kernel.org/patch/10964097/

The above patch #2 let runtime PM framework manage and prevent
concurrent runtime operations in device driver.

And then using patch #1 (this patch) to block general I/O requests after
ufshcd device is resumed.

Thanks,
Stanley Chu


> Thanks,
> 
> Can Guo.
> 
> > This breaks the assumption that UFS PM flows can not be running
> > concurrently and some unexpected racing behavior may happen.
> > 
> > Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
> > ---
> >  drivers/scsi/ufs/ufshcd.c | 29 +++++++++++++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> > 
> > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > index 9d180da77488..2e18596f3a8e 100644
> > --- a/drivers/scsi/ufs/ufshcd.c
> > +++ b/drivers/scsi/ufs/ufshcd.c
> > @@ -159,6 +159,12 @@ struct ufs_pm_lvl_states ufs_pm_lvl_states[] = {
> >  	{UFS_POWERDOWN_PWR_MODE, UIC_LINK_OFF_STATE},
> >  };
> > 
> > +#define ufshcd_scsi_for_each_sdev(fn) \
> > +	list_for_each_entry(starget, &hba->host->__targets, siblings) { \
> > +		__starget_for_each_device(starget, NULL, \
> > +					  fn); \
> > +	}
> > +
> >  static inline enum ufs_dev_pwr_mode
> >  ufs_get_pm_lvl_to_dev_pwr_mode(enum ufs_pm_level lvl)
> >  {
> > @@ -8620,6 +8626,13 @@ int ufshcd_runtime_idle(struct ufs_hba *hba)
> >  }
> >  EXPORT_SYMBOL(ufshcd_runtime_idle);
> > 
> > +static void ufshcd_quiesce_sdev(struct scsi_device *sdev, void *data)
> > +{
> > +	/* Suspended devices are already quiesced so can be skipped */
> > +	if (!pm_runtime_suspended(&sdev->sdev_gendev))
> > +		scsi_device_quiesce(sdev);
> > +}
> > +
> >  /**
> >   * ufshcd_shutdown - shutdown routine
> >   * @hba: per adapter instance
> > @@ -8631,6 +8644,7 @@ EXPORT_SYMBOL(ufshcd_runtime_idle);
> >  int ufshcd_shutdown(struct ufs_hba *hba)
> >  {
> >  	int ret = 0;
> > +	struct scsi_target *starget;
> > 
> >  	if (!hba->is_powered)
> >  		goto out;
> > @@ -8644,6 +8658,21 @@ int ufshcd_shutdown(struct ufs_hba *hba)
> >  			goto out;
> >  	}
> > 
> > +	/*
> > +	 * Quiesce all SCSI devices to prevent any non-PM requests sending
> > +	 * from block layer during and after shutdown.
> > +	 *
> > +	 * Here we can not use blk_cleanup_queue() since PM requests
> > +	 * (with BLK_MQ_REQ_PREEMPT flag) are still required to be sent
> > +	 * through block layer. Therefore SCSI command queued after the
> > +	 * scsi_target_quiesce() call returned will block until
> > +	 * blk_cleanup_queue() is called.
> > +	 *
> > +	 * Besides, scsi_target_"un"quiesce (e.g., scsi_target_resume) can
> > +	 * be ignored since shutdown is one-way flow.
> > +	 */
> > +	ufshcd_scsi_for_each_sdev(ufshcd_quiesce_sdev);
> > +
> >  	ret = ufshcd_suspend(hba, UFS_SHUTDOWN_PM);
> >  out:
> >  	if (ret)


  reply	other threads:[~2020-07-31  8:23 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 14:01 [PATCH v4] scsi: ufs: Quiesce all scsi devices before shutdown Stanley Chu
2020-07-27  7:30 ` Can Guo
2020-07-31  8:22   ` Stanley Chu [this message]
     [not found]     ` <1d74498da71ba54e23cd82ee6400dbd4@codeaurora.org>
2020-07-31  9:27       ` Stanley Chu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1596183773.17247.60.camel@mtkswgap22 \
    --to=stanley.chu@mediatek.com \
    --cc=Andy.Teng@mediatek.com \
    --cc=Chaotian.Jing@mediatek.com \
    --cc=Chun-hung.Wu@mediatek.com \
    --cc=alim.akhtar@samsung.com \
    --cc=asutoshd@codeaurora.org \
    --cc=avri.altman@wdc.com \
    --cc=beanhuo@micron.com \
    --cc=bvanassche@acm.org \
    --cc=cang@codeaurora.org \
    --cc=cc.chou@mediatek.com \
    --cc=jejb@linux.ibm.com \
    --cc=kuohong.wang@mediatek.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mediatek@lists.infradead.org \
    --cc=linux-scsi@vger.kernel.org \
    --cc=martin.petersen@oracle.com \
    --cc=matthias.bgg@gmail.com \
    --cc=peter.wang@mediatek.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).