Messages in this thread | | | Date | Mon, 15 Jun 2015 10:43:28 +0200 | From | Mason <> | Subject | [Semaphore API] down_interruptible_timeout |
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Hello,
The semaphore API provides several flavors of the down primitive:
down, down_interruptible, down_killable, down_trylock, down_timeout
As far as I can tell, they all call __down_common (except down_trylock, which returns 1 where the others would sleep).
I was looking for a version 1) with a timeout 2) that could be interrupted e.g. down_interruptible_timeout, but it doesn't exist.
It seems
__down_common(sem, TASK_INTERRUPTIBLE, timeout);
would work as expected, no?
Do you know why it is not offered? (Maybe there is a better way to achieve the same thing?)
[POST SCRIPTUM EDIT] I found this 2007 discussion: http://thread.gmane.org/gmane.linux.kernel/498034
At the time, Andrew said "Nobody else has needed to invent new locking infrastructure to do such things and I'd prefer not to do so now." I suppose this is still true :-) [/EDIT]
My use-case is pretty simple:
A) process-context kernel thread fills a FIFO and calls down(&fifo_empty); B) ISR handles the FIFO-empty interrupt with up(&fifo_empty);
However, in case something goes wrong and the interrupt never fires, I don't want the process to be stuck in an uninterruptible sleep.
Perhaps I can set a tiny timeout (e.g. 10 µs) and not worry about the interruptible part for such a small duration? (Hmm, __down_common calls schedule_timeout, which is jiffies-based. I don't think there is a hrtimers flavor. So µs timeouts would be off the table?)
Or I could use the interruptible version, and let the user kill the operation if necessary.
I'd like to hear your comments and suggestions.
Regards.
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