linux-kernel - [PATCH 1/3] atomic: Introduce atomic_fetch

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Date:	Thu, 24 Mar 2016 15:37:59 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 1/3] 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.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 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
-- 
2.7.0