Messages in this thread |  | | | Date | Mon, 29 Oct 2007 12:29:25 -0400 | | From | Jeff Garzik <> | | Subject | Re: [PATCH v4 1/2] SCSI: Asynchronous event notification infrastructure |
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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 :)
> 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...
Jeff
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