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Re: [PATCH 4/5] nptl: Fix sem_wait and sem_timedwait cancellation

On Mon, 2016-09-05 at 20:07 +0200, Torvald Riegel wrote:
> On Mon, 2016-08-22 at 11:27 -0300, Adhemerval Zanella wrote:
> > This patch fixes both sem_wait and sem_timedwait cancellation point for
> > uncontended case.  In this scenario only atomics are involved and thus
> > the futex cancellable call is not issue and a pending cancellation signal
> > is not handled.
> I have added a comment on the BZ explaining why I think this is NOTABUG.

I've looked at the POSIX rationale again, and it seems I was wrong in my
interpretation of what the POSIX spec requires.  I now think that we
need to add the pthread_testcancel call or equivalent.  The patch looks
okay, but please also add a comment to the added pthread_testcancel call
explaining why we need it.  Something like this may be useful:

We need to check whether we need to act upon a cancellation request here
because POSIX specifies that cancellation points "shall occur" in
sem_wait and sem_timedwait, which also means that they need to check
this regardless whether they block or not (unlike "may occur"
functions).  See the POSIX Rationale for this requirement: Section
"Thread Cancellation Overview" in
See for thoughts on why this
may be a suboptimal design.


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