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

[Darren Hart]

Eric Dumazet wrote:

Hi Eric,

Thanks for the prompt review...

> Darren Hart a Ãcrit :

> > -	t.tv64 = restart->futex.time;
> > +	if (restart->futex.flags | FLAGS_HAS_TIMEOUT) {
>
> You probably meant :
>
> if (restart->futex.flags & FLAGS_HAS_TIMEOUT)

Gah! You are correct.  Corrected patch below.


RFC: futex: Add FUTEX_HAS_TIMEOUT flag to restart.futex.flags

From: Darren Hart <dvhltc@xxxxxxxxxx>

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.

Changelog:
V7pre: -Corrected FLAGS_HAS_TIMEOUT flag detection logic per Eric Dumazet
V6: - Initial version

Signed-off-by: Darren Hart <dvhltc@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Sripathi Kodi <sripathik@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: John Stultz <johnstul@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Dinakar Guniguntala <dino@xxxxxxxxxx>
Cc: Ulrich Drepper <drepper@xxxxxxxxxx>
Cc: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Jakub Jelinek <jakub@xxxxxxxxxx>
---

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


diff --git a/kernel/futex.c b/kernel/futex.c
index dd05803..07e314c 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);
}

--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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