Of course, del_timer() and del_timer_sync() are different. What I meant the
latter buys nothing for cancel_delayed_work() (which in fact could be named
try_to_cancel_delayed_work()).
Let's look at (2). cancel_delayed_work() (on top of del_timer()) returns 0,
and this is correct, we failed to cancel the timer, and we don't know whether
work->func() finished, or not.
The current code uses del_timer_sync(). It will also return 0. However, it will
spin waiting for timer->function() to complete. So we are just wasting CPU.
I guess I misunderstood you. Perhaps, you propose a new helper which use
try_to_del_timer_sync(), yes? Unless I missed something, this doesn't help.
Because the return value == -1 should be treated as 0. We failed to stop
the timer, and we can't free dwork.
IOW, currently we should do:
if (!cancel_delayed_work(dwork))
cancel_work_sync(dwork));
The same if we use del_timer(). If we use try_to_del_timer_sync(),
if (cancel_delayed_work(dwork) <= 0)
cancel_work_sync(dwork));
(of course, dwork shouldn't re-arm itself).
Could you clarify if I misunderstood you again?
No, it can't be preempted, it runs in softirq context.
Oleg.
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