Re: [PATCH v4] scsi: ufs: Quiesce all scsi devices before shutdown

[Stanley Chu <stanley.chu@mediatek.com>]

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)