Fix: compat_futex should work-around futex signal-restart kernel bug

[urcu.git] / urcu / futex.h

diff --git a/urcu/futex.h b/urcu/futex.h
index 4d16cfa5201453954dc7e6233372ea6969d23c26..0486ff6a1830f174d7471164a282507a6d1f756c 100644 (file)
--- a/urcu/futex.h
+++ b/urcu/futex.h
@@ -73,7 +73,16 @@ static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
 
        ret = futex(uaddr, op, val, timeout, uaddr2, val3);
        if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
-               return compat_futex_noasync(uaddr, op, val, timeout,
+               /*
+                * The fallback on ENOSYS is the async-safe version of
+                * the compat futex implementation, because the
+                * async-safe compat implementation allows being used
+                * concurrently with calls to futex(). Indeed, sys_futex
+                * FUTEX_WAIT, on some architectures (mips and parisc),
+                * within a given process, spuriously return ENOSYS due
+                * to signal restart bugs on some kernel versions.
+                */
+               return compat_futex_async(uaddr, op, val, timeout,
                                uaddr2, val3);
        }
        return ret;