[openib-general] [PATCH] RDMA/iwcm: Get rid of extra call to list_empty()

[Krishna Kumar2]

Hi Tom,

> No, to understand why go look at the implementation of queue_work. BTW, 
this

I was describing the implementation of queue_work() in my
previous mail. So sorry to be dense, but I do not understand
why this patch introduces a race. Can you explain the race
that you had found ? What I understood of queue_work() is :

If cm_work_handler() is already running and processing the
last entry at the same time this new entry was added, it is
guaranteed to find this new entry in it's current run iteration,
and process it. The only issue is with the extra queue_work
by iwcm parallely on a different cpu for the same case.

So if iwcm had done a redundant "queue_work" on this queue,
which, besides adding the new entry to the workqueue, also
does a wakeup of "worker_thread" (which is still running the
previous iteration of run_workqueue -> cm_work_handler).
I am assuming that the wake up function is 
default_wake_function(), since I couldn't locate in wait* code
where this is initialized.

When cm_work_handler finishes removing this new entry, it
returns to worker_thread, which will do a schedule() and
sleep till it is woken up again (since default_wake_function
found that the thread is already running and had done
nothing). Are you referring to a race where the queue_work
is done between the time cm_work_handler finished running
and before it gets back to schedule ? I feel that should not
matter as the run_workqueue() will find this entry in it's
cwq->worklist and continue processing instead of exiting to
worker_thread() and schedule().

Still confused about the race :)

Thanks,

- KK