Hello, (cc'ing linux-scsi) On Wed, Sep 25, 2013 at 01:37:51PM -0700, Anatol Pomozov wrote: > Hi > > On Wed, Sep 4, 2013 at 9:07 AM, Tejun Heo <tj@xxxxxxxxxx> wrote: > > Hello, > > > > On Wed, Sep 04, 2013 at 08:45:33AM -0700, Anatol Pomozov wrote: > >> I am not an expect in block code, so I have a few questions here: > >> > >> - are we sure that this operation is atomic? What if blkg->q becomes > >> dead right after we checked it, and blkg->q->queue_lock got invalid so > >> we have the same crash as before? > > > > request_queue lock switching is something inherently broken in block > > layer. It's unsalvageable. > > Fully agree. The problem that request_queue->queue_lock is a shared > resource that concurrently modified/accessed. In this case (when one > thread changes, another thread access it) we need synchronization to > prevent race conditions. So we need a spin_lock to access queue_lock > spin_lock, otherwise we have a crash like one above... > > > Maybe we can drop lock switching once blk-mq is fully merged. > > Could you please provide more information about it? What is the timeline? I have no idea. Hopefully, not too far out. Jens would have better idea. > If there is an easy way to fix the race condition I would like to > help. Please give me some pointer what direction I should move. The first step would be identifying who are actually making use of lock switching, why and how much difference it would make for them to not do that. > PS Just a little bit of context why I care about this bug. We test a > large farm that actively uses iscsi. We are going to have a lot of > iscsi device startup/shutdown. I am testing whether this codepath has > race conditions and I found one above. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
