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Re: [dm-devel] [PATCH 8/8] dm-mpath: do not activate failed paths



On 02/28/2014 09:49 AM, Junichi Nomura wrote:
> On 02/27/14 16:30, Hannes Reinecke wrote:
>> activate_path() is run without a lock, so the path might be
>> set to failed before activate_path() had a chance to run.
>>
>> Signed-off-by: Hannes Reinecke <hare suse de>
>> ---
>>  drivers/md/dm-mpath.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
>> index 0a40fa9..22e7365 100644
>> --- a/drivers/md/dm-mpath.c
>> +++ b/drivers/md/dm-mpath.c
>> @@ -1196,8 +1196,11 @@ static void activate_path(struct work_struct *work)
>>  	struct pgpath *pgpath =
>>  		container_of(work, struct pgpath, activate_path.work);
>>  
>> -	scsi_dh_activate(bdev_get_queue(pgpath->path.dev->bdev),
>> -				pg_init_done, pgpath);
>> +	if (pgpath->is_active)
>> +		scsi_dh_activate(bdev_get_queue(pgpath->path.dev->bdev),
>> +				 pg_init_done, pgpath);
>> +	else
>> +		pg_init_done(pgpath, SCSI_DH_DEV_OFFLINED);
> 
> Hi Hannes,
> 
> What problem are you going to fix with this?
> It is still possible that the path is set to failed just after
> "if (pgpath->is_active)" and before "scsi_dh_activate".
> 
activate_path() is run from a workqueue, so there is a race window
between the check ->is_active in __pg_init_all_paths() and the time
the scsi_dh_activate() is executed. And as activate_path)() is run
without any locks we don't have any synchronization with fail_path().
So it's well possible that a path gets failed in between
__pg_init_all_paths() and activate_paths().
Granted, we could remove the check for ->is_active in
__pg_init_all_paths(), but I wanted to avoid scheduling a workqueue
item which is known to be failing.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare suse de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)


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