path: root/kernel/futex_compat.c
diff options
authorThomas Gleixner <>2008-02-01 17:45:14 +0100
committerIngo Molnar <>2008-02-01 17:45:14 +0100
commitcd689985cf49f6ff5c8eddc48d98b9d581d9475d (patch)
treea1a119402f5208c45c21b855e8d2fbbaf18cfd72 /kernel/futex_compat.c
parent83e96c604e781098a2f61b8a294919bcf3abfab4 (diff)
futex: Add bitset conditional wait/wakeup functionality
To allow the implementation of optimized rw-locks in user space, glibc needs a possibility to select waiters for wakeup depending on a bitset mask. This requires two new futex OPs: FUTEX_WAIT_BITS and FUTEX_WAKE_BITS These OPs are basically the same as FUTEX_WAIT and FUTEX_WAKE plus an additional argument - a bitset. Further the FUTEX_WAIT_BITS OP is expecting an absolute timeout value instead of the relative one, which is used for the FUTEX_WAIT OP. FUTEX_WAIT_BITS calls into the kernel with a bitset. The bitset is stored in the futex_q structure, which is used to enqueue the waiter into the hashed futex waitqueue. FUTEX_WAKE_BITS also calls into the kernel with a bitset. The wakeup function logically ANDs the bitset with the bitset stored in each waiters futex_q structure. If the result is zero (i.e. none of the set bits in the bitsets is matching), then the waiter is not woken up. If the result is not zero (i.e. one of the set bits in the bitsets is matching), then the waiter is woken. The bitset provided by the caller must be non zero. In case the provided bitset is zero the kernel returns EINVAL. Internaly the new OPs are only extensions to the existing FUTEX_WAIT and FUTEX_WAKE functions. The existing OPs hand a bitset with all bits set into the futex_wait() and futex_wake() functions. Signed-off-by: Thomas Gleixner <> Signed-off-by: Ingo Molnar <>
Diffstat (limited to 'kernel/futex_compat.c')
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 0a43def6fee7..133d558db452 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -167,7 +167,8 @@ asmlinkage long compat_sys_futex(u32 __user *uaddr, int op, u32 val,
int val2 = 0;
int cmd = op & FUTEX_CMD_MASK;
- if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI)) {
+ if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
+ cmd == FUTEX_WAIT_BITSET)) {
if (get_compat_timespec(&ts, utime))
return -EFAULT;
if (!timespec_valid(&ts))