Re: [PATCH v3] scsi/sd: release scan_mutex during sync_cache and start_stop
> On Feb 8, 2017, at 2:58 PM, Bart Van Assche> wrote: > > On Wed, 2017-02-08 at 14:53 -0800, Song Liu wrote: >> +try_lock_scan_mutex = mutex_trylock(>scan_mutex); > > This is at least as bad as the approach of your previous patch because > whether or not this mutex_trylock() call succeeds not only depends on > whether or not the caller holds the scan_mutex but also on whether any > other thread accidentally holds that mutex. Please stop hacking and do > what Christoph proposed, namely address the caller of this method. > > Bart. > Western Digital Corporation (and its subsidiaries) E-mail Confidentiality > Notice & Disclaimer: > > This e-mail and any files transmitted with it may contain confidential or > legally privileged information of WDC and/or its affiliates, and are intended > solely for the use of the individual or entity to which they are addressed. > If you are not the intended recipient, any disclosure, copying, distribution > or any action taken or omitted to be taken in reliance on it, is prohibited. > If you have received this e-mail in error, please notify the sender > immediately and delete the e-mail in its entirety from your system. > Thanks for the feedback. I will dig more in the caller side. Song
Re: [PATCH v3] scsi/sd: release scan_mutex during sync_cache and start_stop
On Wed, 2017-02-08 at 14:53 -0800, Song Liu wrote: > + try_lock_scan_mutex = mutex_trylock(>scan_mutex); This is at least as bad as the approach of your previous patch because whether or not this mutex_trylock() call succeeds not only depends on whether or not the caller holds the scan_mutex but also on whether any other thread accidentally holds that mutex. Please stop hacking and do what Christoph proposed, namely address the caller of this method. Bart.
Re: [PATCH v3] scsi/sd: release scan_mutex during sync_cache and start_stop
> On Feb 8, 2017, at 2:53 PM, Song Liuwrote: > > When a device is deleted through sysfs handle "delete", the code > locks shost->scan_mutex. If multiple devices are deleted at the > same time, these deletes will be handled in series. > > On the other hand, sd_shutdown() sometimes issues long latency > commands: sync cache and start_stop. It is not necessary for these > commands to run in series. > > To reduce latency of parallel "delete" requests, this patch unlock > shost->scan_mutex before long latency commands and relock the mutex > after the command. > > Fixed bug from previous version. > > Reported-by: kernel test robot > Signed-off-by: Song Liu > --- > drivers/scsi/sd.c | 14 ++ > 1 file changed, 14 insertions(+) > > diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c > index 9e0783b..14c5815 100644 > --- a/drivers/scsi/sd.c > +++ b/drivers/scsi/sd.c > @@ -3304,6 +3304,9 @@ static int sd_start_stop_device(struct scsi_disk *sdkp, > int start) > static void sd_shutdown(struct device *dev) > { > struct scsi_disk *sdkp = dev_get_drvdata(dev); > + struct scsi_device *sdev; > + struct Scsi_Host *shost; > + int try_lock_scan_mutex; > > if (!sdkp) > return; /* this can happen */ > @@ -3311,15 +3314,26 @@ static void sd_shutdown(struct device *dev) > if (pm_runtime_suspended(dev)) > return; > > + sdev = sdkp->device; > + shost = sdev->host; > + try_lock_scan_mutex = mutex_trylock(>scan_mutex); > + > if (sdkp->WCE && sdkp->media_present) { > + mutex_unlock(>scan_mutex); > sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n"); > sd_sync_cache(sdkp); > + mutex_lock(>scan_mutex); > } > > if (system_state != SYSTEM_RESTART && sdkp->device->manage_start_stop) { > + mutex_unlock(>scan_mutex); > sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n"); > sd_start_stop_device(sdkp, 0); > + mutex_lock(>scan_mutex); > } > + > + if (try_lock_scan_mutex) > + mutex_unlock(>scan_mutex); > } > > static int sd_suspend_common(struct device *dev, bool ignore_stop_errors) > -- > 2.9.3 > Forgot to CC Christoph
[PATCH v3] scsi/sd: release scan_mutex during sync_cache and start_stop
When a device is deleted through sysfs handle "delete", the code locks shost->scan_mutex. If multiple devices are deleted at the same time, these deletes will be handled in series. On the other hand, sd_shutdown() sometimes issues long latency commands: sync cache and start_stop. It is not necessary for these commands to run in series. To reduce latency of parallel "delete" requests, this patch unlock shost->scan_mutex before long latency commands and relock the mutex after the command. Fixed bug from previous version. Reported-by: kernel test robotSigned-off-by: Song Liu --- drivers/scsi/sd.c | 14 ++ 1 file changed, 14 insertions(+) diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index 9e0783b..14c5815 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -3304,6 +3304,9 @@ static int sd_start_stop_device(struct scsi_disk *sdkp, int start) static void sd_shutdown(struct device *dev) { struct scsi_disk *sdkp = dev_get_drvdata(dev); + struct scsi_device *sdev; + struct Scsi_Host *shost; + int try_lock_scan_mutex; if (!sdkp) return; /* this can happen */ @@ -3311,15 +3314,26 @@ static void sd_shutdown(struct device *dev) if (pm_runtime_suspended(dev)) return; + sdev = sdkp->device; + shost = sdev->host; + try_lock_scan_mutex = mutex_trylock(>scan_mutex); + if (sdkp->WCE && sdkp->media_present) { + mutex_unlock(>scan_mutex); sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n"); sd_sync_cache(sdkp); + mutex_lock(>scan_mutex); } if (system_state != SYSTEM_RESTART && sdkp->device->manage_start_stop) { + mutex_unlock(>scan_mutex); sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n"); sd_start_stop_device(sdkp, 0); + mutex_lock(>scan_mutex); } + + if (try_lock_scan_mutex) + mutex_unlock(>scan_mutex); } static int sd_suspend_common(struct device *dev, bool ignore_stop_errors) -- 2.9.3