On Mon, 2007-10-29 at 12:29 -0400, Jeff Garzik wrote: > James Bottomley wrote: > > On Mon, 2007-10-29 at 12:07 -0400, Jeff Garzik wrote: > >> James Bottomley wrote: > >>> This still doesn't solve the fundamental corruption problem: > >>> sdev->event_work has to contain the work entry until the workqueue has > >>> finished executing it (which is some unspecified time in the future). > >>> As soon as you drop the sdev->list_lock, the system thinks > >>> sdev->event_work is available for reuse. If we fire another event > >>> before the work queue finished processing the prior event, the queue > >>> will be corrupted. > >> I think you're misunderstanding the workqueue code? You can call > >> schedule_work(&sdev->event_work) from anywhere, any time you like, as > >> many times as you like. > > > > OK, take me through it slowly then ... I think schedule_work(work) > > inserts work->entry onto the workqueue list (in > > workqueue.c:insert_work()). If the event hasn't fired, it will already > > be on the list, so adding the same entry to a list twice causes a list > > corruption problem. > > It does a test_and_set_bit() first thing in queue_work(). Similar > exclusivity logic is found in net device land. Ah, the fun of locking > without locks that benh grumbles about :) Ah, OK, sorry ... I was actually looking at __queue_work(). > > Plus, unfortunately, the CC/UA events are going to have to carry extra > > sense data; they're not simply going to be triggers saying something > > happened. > > OK this is a fair criticism. > > If additional data must be carried, then I must ditch the beloved bitmap > implementation and go back to a list (with associated GFP_ATOMIC alloc). > > I will fix this, unless I receive email to the contrary... Yes, unfortunately, thanks. If all events were a simple number, it's easy, but the CC/UA events carry data as well. 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
