James Bottomley wrote: > On Wed, 2016-02-03 at 23:38 +0100, Sebastian Herbszt wrote: > > James Bottomley wrote: > > > On Mon, 2016-02-01 at 19:43 -0800, Bart Van Assche wrote: > > > > On 01/19/16 17:03, James Bottomley wrote: > > > > > On Tue, 2016-01-19 at 19:30 -0500, Martin K. Petersen wrote: > > > > > > > > > > > "Bart" == Bart Van Assche < > > > > > > > > > > > bart.vanassche@xxxxxxxxxxx> > > > > > > > > > > > writes: > > > > > > > > > > > > Bart> Instead of representing the states "visible in sysfs" > > > > > > and > > > > > > "has > > > > > > Bart> been removed from the target list" by a single state > > > > > > variable, > > > > > > use > > > > > > Bart> two variables to represent this information. > > > > > > > > > > > > James: Are you happy with the latest iteration of this? > > > > > > Should I > > > > > > queue > > > > > > it? > > > > > > > > > > Well, I'm OK with the patch: it's a simple transformation of > > > > > the > > > > > enumerated state to a two bit state. What I can't see is how > > > > > it > > > > > fixes > > > > > any soft lockup. > > > > > > > > > > The only change from the current workflow is that the DEL > > > > > transition > > > > > (now the reaped flag) is done before the spin lock is dropped > > > > > which > > > > > would fix a tiny window for two threads both trying to remove > > > > > the > > > > > same > > > > > target, but there's nothing that could possibly fix an > > > > > iterative > > > > > soft > > > > > lockup caused by restarting the loop, which is what the > > > > > changelog > > > > > says. > > > > > > > > Hello James, > > > > > > > > scsi_remove_target() doesn't lock the scan_mutex which means that > > > > concurrent SCSI scanning activity is not prohibited. Such > > > > scanning > > > > activity can postpone the transition of the state of a SCSI > > > > target > > > > into STARGET_DEL. I think if the scheduler decides to run the > > > > thread > > > > that executes scsi_remove_target() on the same CPU as the > > > > scanning > > > > code after the scanning code has obtained a reap ref and before > > > > the > > > > scanning code has released the reap ref again that the soft > > > > lockup > > > > can be triggered that has been reported by Sebastian Herbszt. > > > > > > OK, I finally understand the scenario; I'm not sure I understand > > > how > > > we're getting concurrent scanning and removal from a simple rmmod > > > ... I > > > take it this is insmod rmmod in a tight loop? > > > > I am able to trigger the soft lockup with this test case run once: > > > > modprobe lpfc > > run fio for 10 seconds > > rmmod lpfc > > > > My test setup involves running qla2xxx in target mode (SCST) and > > lpfc as initiator on the same system with one exported volume. > > Hm, that doesn't seem to involve scanning colliding with removal. > Probably something else is pinning the target for some reason ... > unless there's some instability or constant change on the FC fabric > itself? FC is hotplug, so if devices continually appear and disappear, > they'd effectively cause a scan of the added device to take place even > during the rmmod. > > Anyway, does the last_scan patch fix the issue? > > James That patch does also fix my soft lockup. Sebastian -- 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
