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    SubjectRe: [rfc][patch] futex: restartable futex_wait?
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    On Thu, 2007-03-08 at 18:29 +0100, Ingo Molnar wrote:
    > * Nick Piggin <npiggin@suse.de> wrote:
    >
    > > Hi Ingo,
    > >
    > > I'm seeing an LTP test fail for ltp test sigaction_16_24. Basically,
    > > it tests whether the SA_RESTART flag works for the sem_wait operation.

    Not sure, whether the testcase is correct or not. See below

    > > I see sem_wait is implemented with futex_wait, so I wonder whether we
    > > can make it restartable? Am I going about it the right way? (Seems to
    > > fix the testcase here).
    >
    > i think that's quite right. I'm wondering why this never came up before?
    > But your fix is not complete i think:
    >
    > > + restart->arg2 = time;
    > > + return -ERESTART_RESTARTBLOCK;
    > > + }
    >
    > 'time' here is relative, so the restarted syscall will do a /full/ wait
    > again.
    >
    > maybe we should rather convert futex timed-waits to hrtimers? Thomas?

    The problem is that the original API is based on relative time and
    therefor can not be changed.

    sem_wait returns -EINTR to the application when it is interrupted, while
    pthread_mutex_lock does not.

    http://www.opengroup.org/onlinepubs/009695399/functions/sem_wait.html

    http://www.opengroup.org/onlinepubs/009695399/functions/pthread_mutex_lock.html

    We need to create a seperate op for the futex - just like the pi_futex
    and use absolute time there too.

    tglx


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