The VMA tests need an operation equivalent to atomic_inc_unless_negative() to implement a fake mapping_map_writable(). Adding it will enable them to switch to the shared atomic headers and simplify that fake implementation. In order to add that, also add atomic_try_cmpxchg() which can be used to implement it. This is copied from Documentation/atomic_t.txt. Then, implement atomic_inc_unless_negative() itself based on the raw_atomic_dec_unless_positive() in include/linux/atomic/atomic-arch-fallback.h. There's no present need for a highly-optimised version of this (nor any reason to think this implementation is sub-optimal on x86) so just implement this with generic C, no x86-specifics. Signed-off-by: Brendan Jackman --- tools/include/linux/atomic.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/tools/include/linux/atomic.h b/tools/include/linux/atomic.h index 01907b33537e04c5e860dd2cd61a61dfab6ea8f1..50c66ba9ada58cf05125e2e2472734bf3b0f8595 100644 --- a/tools/include/linux/atomic.h +++ b/tools/include/linux/atomic.h @@ -12,4 +12,26 @@ void atomic_long_set(atomic_long_t *v, long i); #define atomic_cmpxchg_release atomic_cmpxchg #endif /* atomic_cmpxchg_relaxed */ +static inline bool atomic_try_cmpxchg(atomic_t *ptr, int *oldp, int new) +{ + int ret, old = *oldp; + + ret = atomic_cmpxchg(ptr, old, new); + if (ret != old) + *oldp = ret; + return ret == old; +} + +static inline bool atomic_inc_unless_negative(atomic_t *v) +{ + int c = atomic_read(v); + + do { + if (unlikely(c < 0)) + return false; + } while (!atomic_try_cmpxchg(v, &c, c + 1)); + + return true; +} + #endif /* __TOOLS_LINUX_ATOMIC_H */ -- 2.50.1