On 11.08.2015 11:15, Oliver Neukum wrote: > On Mon, 2015-08-03 at 16:07 +0300, Mathias Nyman wrote: >> From: Gavin Shan <gwshan@xxxxxxxxxxxxxxxxxx> >> >> When xhci_mem_cleanup() is called, it's possible that the command >> timer isn't initialized and scheduled. For those cases, to delete >> the command timer causes soft-lockup as below stack dump shows. >> >> The patch avoids deleting the command timer if it's not scheduled >> with the help of timer_pending(). > > Are you sure this is safe? timer_pending() will not show you that > the timer function is running. It looks like you introduced a race > between timeout and cleanup. > Looking at it in more detail you're right. Fortunately this can only happen in cases where xhci is already hosed (no command response for 5 seconds), and we are at the same time anyway about to remove xhci. Doesn't this mean that all cases with if (timer_pending(&timer)) del_timer_sync(&timer) is just basically the same as a plain del_timer(&timer)? Anyways, turns out that the error path in xhci initialization code can end up calling del_timer_sync() before timer is initialized. This should be fixed by re-arranging some code in xhci initialization instead. Greg, should this be reverted in rc7? I think that the possible side effect of this patch is still lesser the original issue. Thanks for spotting this -Mathias -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
