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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