[dm-devel] [PATCH v2 1/7] libmultipath: fix tur checker locking

[Martin Wilck]

On Thu, 2018-02-08 at 17:56 -0600, Benjamin Marzinski wrote:
> ct->running is now an atomic variable.  When the thread is started
> it is set to 1. When the checker wants to kill a thread, it
> atomically
> sets the value to 0 and reads the previous value.  If it was 1,
> the checker cancels the thread. If it was 0, the nothing needs to be
> done.  After the checker has dealt with the thread, it sets ct-
> >thread
> to NULL.
> 
> When the thread is done, it atomicalllys sets the value of ct-
> >running
> to 0 and reads the previous value. If it was 1, the thread just
> exits.
> If it was 0, then the checker is trying to cancel the thread, and so
> the thread calls pause(), which is a cancellation point.
> 

I'm missing one thing here. My poor brain is aching.

cleanup_func() can be entered in two ways: a) if the thread has been
cancelled and passed a cancellation point already, or b) if it exits
normally and calls pthread_cleanup_pop(). 
In case b), waiting for the cancellation request by calling pause()
makes sense to me. But in case a), the thread has already seen the
cancellation request - wouldn't calling pause() cause it to sleep
forever?

Martin

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