diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2021-04-22 22:44:23 +0300 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-06-22 17:42:09 +0300 |
| commit | bf22a6976897977b0a3f1aeba6823c959fc4fdae (patch) | |
| tree | 7cc9e19e17e0e2c9812b41e56bc623aea4688c75 /include/uapi/linux/futex.h | |
| parent | e112c41341c03d9224a9fc522bdb3539bc849b56 (diff) | |
| download | linux-bf22a6976897977b0a3f1aeba6823c959fc4fdae.tar.xz | |
futex: Provide FUTEX_LOCK_PI2 to support clock selection
The FUTEX_LOCK_PI futex operand uses a CLOCK_REALTIME based absolute
timeout since it was implemented, but it does not require that the
FUTEX_CLOCK_REALTIME flag is set, because that was introduced later.
In theory as none of the user space implementations can set the
FUTEX_CLOCK_REALTIME flag on this operand, it would be possible to
creatively abuse it and make the meaning invers, i.e. select CLOCK_REALTIME
when not set and CLOCK_MONOTONIC when set. But that's a nasty hackery.
Another option would be to have a new FUTEX_CLOCK_MONOTONIC flag only for
FUTEX_LOCK_PI, but that's also awkward because it does not allow libraries
to handle the timeout clock selection consistently.
So provide a new FUTEX_LOCK_PI2 operand which implements the timeout
semantics which the other operands use and leave FUTEX_LOCK_PI alone.
Reported-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210422194705.440773992@linutronix.de
Diffstat (limited to 'include/uapi/linux/futex.h')
| -rw-r--r-- | include/uapi/linux/futex.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/include/uapi/linux/futex.h b/include/uapi/linux/futex.h index a89eb0accd5e..235e5b2facaa 100644 --- a/include/uapi/linux/futex.h +++ b/include/uapi/linux/futex.h @@ -21,6 +21,7 @@ #define FUTEX_WAKE_BITSET 10 #define FUTEX_WAIT_REQUEUE_PI 11 #define FUTEX_CMP_REQUEUE_PI 12 +#define FUTEX_LOCK_PI2 13 #define FUTEX_PRIVATE_FLAG 128 #define FUTEX_CLOCK_REALTIME 256 @@ -32,6 +33,7 @@ #define FUTEX_CMP_REQUEUE_PRIVATE (FUTEX_CMP_REQUEUE | FUTEX_PRIVATE_FLAG) #define FUTEX_WAKE_OP_PRIVATE (FUTEX_WAKE_OP | FUTEX_PRIVATE_FLAG) #define FUTEX_LOCK_PI_PRIVATE (FUTEX_LOCK_PI | FUTEX_PRIVATE_FLAG) +#define FUTEX_LOCK_PI2_PRIVATE (FUTEX_LOCK_PI2 | FUTEX_PRIVATE_FLAG) #define FUTEX_UNLOCK_PI_PRIVATE (FUTEX_UNLOCK_PI | FUTEX_PRIVATE_FLAG) #define FUTEX_TRYLOCK_PI_PRIVATE (FUTEX_TRYLOCK_PI | FUTEX_PRIVATE_FLAG) #define FUTEX_WAIT_BITSET_PRIVATE (FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG) |