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    Subject[tip PATCH v6 6/8] RFC: futex: Add FUTEX_HAS_TIMEOUT flag to restart.futex.flags
    Date
    Currently restart is only used if there is a timeout.  The requeue_pi
    functionality requires restarting to futex_lock_pi() on signal after
    wakeup in futex_wait_requeue_pi() regardless of if there was a timeout
    or not. Using 0 for the timeout value is confusing as that could
    indicate an expired timer. The flag makes this explicit.

    Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Sripathi Kodi <sripathik@in.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: John Stultz <johnstul@us.ibm.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Dinakar Guniguntala <dino@in.ibm.com>
    Cc: Ulrich Drepper <drepper@redhat.com>
    Cc: Eric Dumazet <dada1@cosmosbay.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Jakub Jelinek <jakub@redhat.com>
    ---

    kernel/futex.c | 12 ++++++++----
    1 files changed, 8 insertions(+), 4 deletions(-)

    diff --git a/kernel/futex.c b/kernel/futex.c
    index dd05803..f54faf5 100644
    --- a/kernel/futex.c
    +++ b/kernel/futex.c
    @@ -1254,6 +1254,7 @@ handle_fault:
    */
    #define FLAGS_SHARED 0x01
    #define FLAGS_CLOCKRT 0x02
    +#define FLAGS_HAS_TIMEOUT 0x04

    static long futex_wait_restart(struct restart_block *restart);

    @@ -1493,7 +1494,7 @@ retry_private:
    restart->futex.val = val;
    restart->futex.time = abs_time->tv64;
    restart->futex.bitset = bitset;
    - restart->futex.flags = 0;
    + restart->futex.flags = FLAGS_HAS_TIMEOUT;

    if (fshared)
    restart->futex.flags |= FLAGS_SHARED;
    @@ -1517,13 +1518,16 @@ static long futex_wait_restart(struct restart_block *restart)
    {
    u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
    int fshared = 0;
    - ktime_t t;
    + ktime_t t, *tp = NULL;

    - t.tv64 = restart->futex.time;
    + if (restart->futex.flags | FLAGS_HAS_TIMEOUT) {
    + t.tv64 = restart->futex.time;
    + tp = &t;
    + }
    restart->fn = do_no_restart_syscall;
    if (restart->futex.flags & FLAGS_SHARED)
    fshared = 1;
    - return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,
    + return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
    restart->futex.bitset,
    restart->futex.flags & FLAGS_CLOCKRT);
    }


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