[tip PATCH v7 6/9] RFC: futex: Add FUTEX_HAS_TIMEOUT flag to restart.futex.flags

Darren Hart
2009-04-03T20:42:12Z

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. While the check is not technically needed in
futex_wait_restart(), doing so makes the code consistent with and will avoid
confusion should the need arise to restart wait without a timeout.

Changelog:
V7: -Corrected FLAGS_HAS_TIMEOUT flag detection logic per Eric Dumazet
V6: - Initial version

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 c2b58d8..04e5431 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1252,6 +1252,7 @@ handle_fault:
*/
#define FLAGS_SHARED 0x01
#define FLAGS_CLOCKRT 0x02
+#define FLAGS_HAS_TIMEOUT 0x04

static long futex_wait_restart(struct restart_block *restart);

@@ -1486,7 +1487,7 @@ 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;
@@ -1510,13 +1511,16 @@ 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);
}