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| author | Thomas Gleixner <tglx@linutronix.de> | 2021-04-22 21:44:23 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-06-22 16:42:09 +0200 |
| commit | bf22a6976897977b0a3f1aeba6823c959fc4fdae (patch) | |
| tree | 7cc9e19e17e0e2c9812b41e56bc623aea4688c75 /kernel/futex.c | |
| parent | e112c41341c03d9224a9fc522bdb3539bc849b56 (diff) | |
| download | linux-bf22a6976897977b0a3f1aeba6823c959fc4fdae.tar.gz | |
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.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index f820439a8aae7..f832b64346256 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; |