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authorThomas Gleixner <tglx@linutronix.de>2021-04-22 21:44:23 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-06-22 16:42:09 +0200
commitbf22a6976897977b0a3f1aeba6823c959fc4fdae (patch)
tree7cc9e19e17e0e2c9812b41e56bc623aea4688c75 /kernel/futex.c
parente112c41341c03d9224a9fc522bdb3539bc849b56 (diff)
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 'kernel/futex.c')
-rw-r--r--kernel/futex.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index f820439a8aae..f832b6434625 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3707,12 +3707,14 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
if (op & FUTEX_CLOCK_REALTIME) {
flags |= FLAGS_CLOCKRT;
- if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
+ if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
+ cmd != FUTEX_LOCK_PI2)
return -ENOSYS;
}
switch (cmd) {
case FUTEX_LOCK_PI:
+ case FUTEX_LOCK_PI2:
case FUTEX_UNLOCK_PI:
case FUTEX_TRYLOCK_PI:
case FUTEX_WAIT_REQUEUE_PI:
@@ -3740,6 +3742,8 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
case FUTEX_LOCK_PI:
flags |= FLAGS_CLOCKRT;
+ fallthrough;
+ case FUTEX_LOCK_PI2:
return futex_lock_pi(uaddr, flags, timeout, 0);
case FUTEX_UNLOCK_PI:
return futex_unlock_pi(uaddr, flags);
@@ -3760,6 +3764,7 @@ static __always_inline bool futex_cmd_has_timeout(u32 cmd)
switch (cmd) {
case FUTEX_WAIT:
case FUTEX_LOCK_PI:
+ case FUTEX_LOCK_PI2:
case FUTEX_WAIT_BITSET:
case FUTEX_WAIT_REQUEUE_PI:
return true;