The current semantics for futex_wake() are a bit loose, specifically asking for 0 futexes to be woken actually gets you 1. Adding a !nr check to sys_futex_wake() makes that it would return 0 for unaligned futex words, because that check comes in the shared futex_wake() function. Adding the !nr check there, would affect the legacy sys_futex() semantics. Hence frob a flag :-( Suggested-by: André Almeida <andrealmeid@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> --- Index: linux-2.6/kernel/futex/futex.h =================================================================== --- linux-2.6.orig/kernel/futex/futex.h +++ linux-2.6/kernel/futex/futex.h @@ -17,25 +17,26 @@ * Futex flags used to encode options to functions and preserve them across * restarts. */ -#define FLAGS_SIZE_8 0x00 -#define FLAGS_SIZE_16 0x01 -#define FLAGS_SIZE_32 0x02 -#define FLAGS_SIZE_64 0x03 +#define FLAGS_SIZE_8 0x0000 +#define FLAGS_SIZE_16 0x0001 +#define FLAGS_SIZE_32 0x0002 +#define FLAGS_SIZE_64 0x0003 -#define FLAGS_SIZE_MASK 0x03 +#define FLAGS_SIZE_MASK 0x0003 #ifdef CONFIG_MMU -# define FLAGS_SHARED 0x10 +# define FLAGS_SHARED 0x0010 #else /* * NOMMU does not have per process address space. Let the compiler optimize * code away. */ -# define FLAGS_SHARED 0x00 +# define FLAGS_SHARED 0x0000 #endif -#define FLAGS_CLOCKRT 0x20 -#define FLAGS_HAS_TIMEOUT 0x40 -#define FLAGS_NUMA 0x80 +#define FLAGS_CLOCKRT 0x0020 +#define FLAGS_HAS_TIMEOUT 0x0040 +#define FLAGS_NUMA 0x0080 +#define FLAGS_STRICT 0x0100 /* FUTEX_ to FLAGS_ */ static inline unsigned int futex_to_flags(unsigned int op) Index: linux-2.6/kernel/futex/syscalls.c =================================================================== --- linux-2.6.orig/kernel/futex/syscalls.c +++ linux-2.6/kernel/futex/syscalls.c @@ -333,7 +333,7 @@ SYSCALL_DEFINE4(futex_wake, if (!futex_validate_input(flags, mask)) return -EINVAL; - return futex_wake(uaddr, flags, nr, mask); + return futex_wake(uaddr, FLAGS_STRICT | flags, nr, mask); } #ifdef CONFIG_COMPAT Index: linux-2.6/kernel/futex/waitwake.c =================================================================== --- linux-2.6.orig/kernel/futex/waitwake.c +++ linux-2.6/kernel/futex/waitwake.c @@ -155,6 +155,9 @@ int futex_wake(u32 __user *uaddr, unsign if (unlikely(ret != 0)) return ret; + if ((flags & FLAGS_STRICT) && !nr_wake) + return 0; + hb = futex_hash(&key); /* Make sure we really have tasks to wakeup */
