Re: [tip PATCH v6 6/8] RFC: futex: Add FUTEX_HAS_TIMEOUT flag to restart.futex.flags

[Eric Dumazet <dada1@cosmosbay.com>]

Darren Hart a écrit :
> 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) {

You probably meant :

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);
>  }
> 
>