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6428671bae
A while back Viro posted a number of 'interesting' mutex_is_locked() users on IRC, one of those was RCU. RCU seems to use mutex_is_locked() to avoid doing mutex_trylock(), the regular load before modify pattern. While the use isn't wrong per se, its curious in that its needed at all, mutex_trylock() should be good enough on its own to avoid the pointless cacheline bounces. So fix those and remove the mutex_is_locked() (ab)use from RCU. Reported-by: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Paul McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <Waiman.Long@hpe.com> Link: http://lkml.kernel.org/r/20160601185815.GW3190@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
133 lines
3.1 KiB
C
133 lines
3.1 KiB
C
/*
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* Optimised mutex implementation of include/asm-generic/mutex-dec.h algorithm
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*/
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#ifndef _ASM_POWERPC_MUTEX_H
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#define _ASM_POWERPC_MUTEX_H
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static inline int __mutex_cmpxchg_lock(atomic_t *v, int old, int new)
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{
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int t;
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__asm__ __volatile__ (
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"1: lwarx %0,0,%1 # mutex trylock\n\
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cmpw 0,%0,%2\n\
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bne- 2f\n"
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PPC405_ERR77(0,%1)
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" stwcx. %3,0,%1\n\
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bne- 1b"
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PPC_ACQUIRE_BARRIER
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"\n\
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2:"
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: "=&r" (t)
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: "r" (&v->counter), "r" (old), "r" (new)
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: "cc", "memory");
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return t;
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}
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static inline int __mutex_dec_return_lock(atomic_t *v)
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{
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int t;
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__asm__ __volatile__(
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"1: lwarx %0,0,%1 # mutex lock\n\
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addic %0,%0,-1\n"
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PPC405_ERR77(0,%1)
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" stwcx. %0,0,%1\n\
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bne- 1b"
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PPC_ACQUIRE_BARRIER
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: "=&r" (t)
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: "r" (&v->counter)
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: "cc", "memory");
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return t;
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}
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static inline int __mutex_inc_return_unlock(atomic_t *v)
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{
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int t;
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__asm__ __volatile__(
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PPC_RELEASE_BARRIER
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"1: lwarx %0,0,%1 # mutex unlock\n\
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addic %0,%0,1\n"
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PPC405_ERR77(0,%1)
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" stwcx. %0,0,%1 \n\
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bne- 1b"
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: "=&r" (t)
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: "r" (&v->counter)
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: "cc", "memory");
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return t;
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}
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/**
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* __mutex_fastpath_lock - try to take the lock by moving the count
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* from 1 to a 0 value
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* @count: pointer of type atomic_t
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* @fail_fn: function to call if the original value was not 1
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*
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* Change the count from 1 to a value lower than 1, and call <fail_fn> if
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* it wasn't 1 originally. This function MUST leave the value lower than
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* 1 even when the "1" assertion wasn't true.
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*/
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static inline void
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__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
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{
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if (unlikely(__mutex_dec_return_lock(count) < 0))
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fail_fn(count);
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}
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/**
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* __mutex_fastpath_lock_retval - try to take the lock by moving the count
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* from 1 to a 0 value
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* @count: pointer of type atomic_t
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*
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* Change the count from 1 to a value lower than 1. This function returns 0
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* if the fastpath succeeds, or -1 otherwise.
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*/
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static inline int
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__mutex_fastpath_lock_retval(atomic_t *count)
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{
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if (unlikely(__mutex_dec_return_lock(count) < 0))
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return -1;
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return 0;
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}
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/**
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* __mutex_fastpath_unlock - try to promote the count from 0 to 1
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* @count: pointer of type atomic_t
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* @fail_fn: function to call if the original value was not 0
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*
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* Try to promote the count from 0 to 1. If it wasn't 0, call <fail_fn>.
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* In the failure case, this function is allowed to either set the value to
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* 1, or to set it to a value lower than 1.
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*/
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static inline void
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__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
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{
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if (unlikely(__mutex_inc_return_unlock(count) <= 0))
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fail_fn(count);
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}
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#define __mutex_slowpath_needs_to_unlock() 1
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/**
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* __mutex_fastpath_trylock - try to acquire the mutex, without waiting
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*
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* @count: pointer of type atomic_t
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* @fail_fn: fallback function
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*
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* Change the count from 1 to 0, and return 1 (success), or if the count
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* was not 1, then return 0 (failure).
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*/
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static inline int
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__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
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{
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if (likely(atomic_read(count) == 1 && __mutex_cmpxchg_lock(count, 1, 0) == 1))
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return 1;
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return 0;
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}
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#endif
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