locking/atomic: Introduce atomic_fetch_or()

This is deemed to replace the type generic fetch_or() which brings a lot
of issues such as macro induced block variable aliasing and sloppy types.
Not to mention fetch_or() doesn't refer to any namespace, adding even
more confusion.

So lets provide an atomic_t version. Current and next users of fetch_or()
are thus encouraged to use atomic_t.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1458830281-4255-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index df4f369254c0305174f6be6a6caca6b296c692c5..3d64c085216488190088dcc29f63be3b1e0f4dac 100644 (file)
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -558,6 +558,27 @@ static inline int atomic_dec_if_positive(atomic_t *v)
 }
 #endif
 
+/**
+ * atomic_fetch_or - perform *p |= mask and return old value of *p
+ * @p: pointer to atomic_t
+ * @mask: mask to OR on the atomic_t
+ */
+#ifndef atomic_fetch_or
+static inline int atomic_fetch_or(atomic_t *p, int mask)
+{
+       int old, val = atomic_read(p);
+
+       for (;;) {
+               old = atomic_cmpxchg(p, val, val | mask);
+               if (old == val)
+                       break;
+               val = old;
+       }
+
+       return old;
+}
+#endif
+
 /**
  * fetch_or - perform *ptr |= mask and return old value of *ptr
  * @ptr: pointer to value