[tip:core/urgent] locking/atomic: Introduce atomic_fetch_or()

[tip-bot for Frederic Weisbecker]

Commit-ID:  5acba71e18833b9d06686b3751598bfa263a3ac3
Gitweb:     http://git.kernel.org/tip/5acba71e18833b9d06686b3751598bfa263a3ac3
Author:     Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Thu, 24 Mar 2016 15:37:59 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 29 Mar 2016 11:52:11 +0200

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@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1458830281-4255-2-git-send-email-fweisbec@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 include/linux/atomic.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index df4f369..3d64c08 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -559,6 +559,27 @@ 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
  * @mask: mask to OR on the value