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)
next prev parent 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
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