linux-kernel - [tip:core/urgent] locking/atomic, sched: Unexport fetch

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Date:	Tue, 29 Mar 2016 03:37:35 -0700
From:	tip-bot for Frederic Weisbecker <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	mingo@...nel.org, peterz@...radead.org, tglx@...utronix.de,
	fweisbec@...il.com, akpm@...ux-foundation.org, hpa@...or.com
Subject: [tip:core/urgent] locking/atomic, sched: Unexport fetch_or()

Commit-ID:  5529578a27288d11d4d15635c258c6dde0f0fb10
Gitweb:     http://git.kernel.org/tip/5529578a27288d11d4d15635c258c6dde0f0fb10
Author:     Frederic Weisbecker <fweisbec@...il.com>
AuthorDate: Thu, 24 Mar 2016 15:38:01 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 29 Mar 2016 11:52:11 +0200

locking/atomic, sched: Unexport fetch_or()

This patch functionally reverts:

  5fd7a09cfb8c ("atomic: Export fetch_or()")

During the merge Linus observed that the generic version of fetch_or()
was messy:

  " This makes the ugly "fetch_or()" macro that the scheduler used
    internally a new generic helper, and does a bad job at it. "

  e23604edac2a Merge branch 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Now that we have introduced atomic_fetch_or(), fetch_or() is only used
by the scheduler in order to deal with thread_info flags which type
can vary across architectures.

Lets confine fetch_or() back to the scheduler so that we encourage
future users to use the more robust and well typed atomic_t version
instead.

While at it, fetch_or() gets robustified, pasting improvements from a
previous patch by Ingo Molnar that avoids needless expression
re-evaluations in the loop.

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1458830281-4255-4-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/atomic.h | 21 ---------------------
 kernel/sched/core.c    | 18 ++++++++++++++++++
 2 files changed, 18 insertions(+), 21 deletions(-)

diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index 3d64c08..506c353 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -579,27 +579,6 @@ static inline int atomic_fetch_or(atomic_t *p, int mask)
 }
 #endif
 
-/**
- * fetch_or - perform *ptr |= mask and return old value of *ptr
- * @ptr: pointer to value
- * @mask: mask to OR on the value
- *
- * cmpxchg based fetch_or, macro so it works for different integer types
- */
-#ifndef fetch_or
-#define fetch_or(ptr, mask)						\
-({	typeof(*(ptr)) __old, __val = *(ptr);				\
-	for (;;) {							\
-		__old = cmpxchg((ptr), __val, __val | (mask));		\
-		if (__old == __val)					\
-			break;						\
-		__val = __old;						\
-	}								\
-	__old;								\
-})
-#endif
-
-
 #ifdef CONFIG_GENERIC_ATOMIC64
 #include <asm-generic/atomic64.h>
 #endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d8465ee..8b489fc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -321,6 +321,24 @@ static inline void init_hrtick(void)
 }
 #endif	/* CONFIG_SCHED_HRTICK */
 
+/*
+ * cmpxchg based fetch_or, macro so it works for different integer types
+ */
+#define fetch_or(ptr, mask)						\
+	({								\
+		typeof(ptr) _ptr = (ptr);				\
+		typeof(mask) _mask = (mask);				\
+		typeof(*_ptr) _old, _val = *_ptr;			\
+									\
+		for (;;) {						\
+			_old = cmpxchg(_ptr, _val, _val | _mask);	\
+			if (_old == _val)				\
+				break;					\
+			_val = _old;					\
+		}							\
+	_old;								\
+})
+
 #if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
 /*
  * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,