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>
128 lines
3.3 KiB
C
128 lines
3.3 KiB
C
/*
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* Assembly implementation of the mutex fastpath, based on atomic
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* decrement/increment.
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*
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* started by Ingo Molnar:
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*
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* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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*/
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#ifndef _ASM_X86_MUTEX_64_H
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#define _ASM_X86_MUTEX_64_H
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/**
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* __mutex_fastpath_lock - decrement and call function if negative
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* @v: pointer of type atomic_t
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* @fail_fn: function to call if the result is negative
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*
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* Atomically decrements @v and calls <fail_fn> if the result is negative.
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*/
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#ifdef CC_HAVE_ASM_GOTO
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static inline void __mutex_fastpath_lock(atomic_t *v,
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void (*fail_fn)(atomic_t *))
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{
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asm_volatile_goto(LOCK_PREFIX " decl %0\n"
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" jns %l[exit]\n"
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: : "m" (v->counter)
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: "memory", "cc"
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: exit);
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fail_fn(v);
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exit:
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return;
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}
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#else
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#define __mutex_fastpath_lock(v, fail_fn) \
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do { \
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unsigned long dummy; \
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\
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typecheck(atomic_t *, v); \
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typecheck_fn(void (*)(atomic_t *), fail_fn); \
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\
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asm volatile(LOCK_PREFIX " decl (%%rdi)\n" \
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" jns 1f \n" \
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" call " #fail_fn "\n" \
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"1:" \
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: "=D" (dummy) \
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: "D" (v) \
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: "rax", "rsi", "rdx", "rcx", \
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"r8", "r9", "r10", "r11", "memory"); \
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} while (0)
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#endif
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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 __mutex_fastpath_lock_retval(atomic_t *count)
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{
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if (unlikely(atomic_dec_return(count) < 0))
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return -1;
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else
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return 0;
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}
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/**
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* __mutex_fastpath_unlock - increment and call function if nonpositive
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* @v: pointer of type atomic_t
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* @fail_fn: function to call if the result is nonpositive
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*
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* Atomically increments @v and calls <fail_fn> if the result is nonpositive.
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*/
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#ifdef CC_HAVE_ASM_GOTO
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static inline void __mutex_fastpath_unlock(atomic_t *v,
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void (*fail_fn)(atomic_t *))
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{
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asm_volatile_goto(LOCK_PREFIX " incl %0\n"
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" jg %l[exit]\n"
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: : "m" (v->counter)
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: "memory", "cc"
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: exit);
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fail_fn(v);
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exit:
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return;
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}
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#else
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#define __mutex_fastpath_unlock(v, fail_fn) \
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do { \
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unsigned long dummy; \
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\
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typecheck(atomic_t *, v); \
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typecheck_fn(void (*)(atomic_t *), fail_fn); \
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\
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asm volatile(LOCK_PREFIX " incl (%%rdi)\n" \
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" jg 1f\n" \
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" call " #fail_fn "\n" \
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"1:" \
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: "=D" (dummy) \
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: "D" (v) \
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: "rax", "rsi", "rdx", "rcx", \
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"r8", "r9", "r10", "r11", "memory"); \
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} while (0)
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#endif
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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 return 0 (failure)
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* if it wasn't 1 originally. [the fallback function is never used on
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* x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
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*/
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static inline int __mutex_fastpath_trylock(atomic_t *count,
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int (*fail_fn)(atomic_t *))
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{
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if (likely(atomic_read(count) == 1 && atomic_cmpxchg(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 /* _ASM_X86_MUTEX_64_H */
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