> On Feb 8, 2017, at 1:02 PM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> On Wed, Feb 08, 2017 at 12:42:40PM -0800, Song Liu wrote:
>> 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 <fengguang.wu@xxxxxxxxx>
>> Signed-off-by: Song Liu <songliubraving@xxxxxx>
>> ---
>> drivers/scsi/sd.c | 15 +++++++++++++++
>> 1 file changed, 15 insertions(+)
>>
>> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
>> index 9e0783b..22add77 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;
>> + bool scan_mutex_locked;
>>
>> if (!sdkp)
>> return; /* this can happen */
>> @@ -3311,14 +3314,26 @@ static void sd_shutdown(struct device *dev)
>> if (pm_runtime_suspended(dev))
>> return;
>>
>> + sdev = sdkp->device;
>> + shost = sdev->host;
>> + scan_mutex_locked = mutex_is_locked(&shost->scan_mutex);
>
> The use of mutex_is_locked outside of asserts is always bogus.
>
> The fix you want is most like in the caller of the method.
Hi Christoph,
Thanks for the feedback. The other caller (that does not hold scan_mutex)
of sd_shutdown() is device_shutdown() in drivers/base/core.c. I could not
think of a good way to lock scan_mutex there.
Would some variation of mutex_trylock() be a better option here?
Thanks,
Song
