Commit 5529578a authored Mar 24, 2016 by Frederic Weisbecker Committed by Ingo Molnar Mar 29, 2016

locking/atomic, sched: Unexport fetch_or()

This patch functionally reverts:

  5fd7a09c ("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. "

  e23604ed 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@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1458830281-4255-4-git-send-email-fweisbec@gmail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent f009a7a7

include/linux/atomic.h

+0 −21

Original line number	Diff line number	Diff line
		@@ -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

kernel/sched/core.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -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,