On Thu, 2010-05-20 at 17:05 +0200, Tejun Heo wrote: > Hello, > > On 05/20/2010 01:33 PM, Prashant wrote: > > I have a question related to code which is almost same in the > > current kernel. I don't know whether this is the right mailing list > > for the following question. > > linux-scsi would probably fit better (cc'd). > > > When a sata drive is unplugged, its corresponding sdev's state is set > > to SDEV_OFFLINE. Now if IO requests are still comming on the same device, > > They will be killed by calling scsi_kill_request(). > > > > 1) scsi_kill_request does following things: > > i) Unlock request queue > > ii) Increment host_busy count > > iii) Lock request queue > > iv) Calls __scsi_done() > > > > 2) __scsi_done() does following things: > > i) set request completion data > > ii) Calls blk_completion_request() > > > > 3) blk_completion_request() does following things: > > i) Adds request->donelist to blk_cpu_done softirq queue > > and raise the softirq (which is scsi_softirq_done) > > > > 4) next sequence is: > > scsi_softirq_done >> scsi_finish_command >> scsi_device_unbusy() > > > > 5) scsi_device_unbusy() again locks the request_queue. This is the place where > > we can get into the spinlock recursion. > > > > Is this correct? Please correct me if something is wrong. > > Raising softirq defers the work to another context and grabbing the > same lock from softirq handler doesn't constitute a recursive locking. > Please try to reproduce the problem on recent kernel w/ lockdep > enabled. Just to confirm what Tejun says: the design of the cmd -> done (i.e. scsi_done) going through the block sofirq handler is specifically so it can be called either locked or unlocked, so this can never be a recursion. James -- 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
