mirror of
https://github.com/torvalds/linux.git
synced 2024-12-27 21:33:00 +00:00
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
/*
|
|
* Assembly implementation of the mutex fastpath, based on atomic
|
|
* decrement/increment.
|
|
*
|
|
* started by Ingo Molnar:
|
|
*
|
|
* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
|
|
*/
|
|
#ifndef _ASM_X86_MUTEX_64_H
|
|
#define _ASM_X86_MUTEX_64_H
|
|
|
|
/**
|
|
* __mutex_fastpath_lock - decrement and call function if negative
|
|
* @v: pointer of type atomic_t
|
|
* @fail_fn: function to call if the result is negative
|
|
*
|
|
* Atomically decrements @v and calls <fail_fn> if the result is negative.
|
|
*/
|
|
#ifdef CC_HAVE_ASM_GOTO
|
|
static inline void __mutex_fastpath_lock(atomic_t *v,
|
|
void (*fail_fn)(atomic_t *))
|
|
{
|
|
asm_volatile_goto(LOCK_PREFIX " decl %0\n"
|
|
" jns %l[exit]\n"
|
|
: : "m" (v->counter)
|
|
: "memory", "cc"
|
|
: exit);
|
|
fail_fn(v);
|
|
exit:
|
|
return;
|
|
}
|
|
#else
|
|
#define __mutex_fastpath_lock(v, fail_fn) \
|
|
do { \
|
|
unsigned long dummy; \
|
|
\
|
|
typecheck(atomic_t *, v); \
|
|
typecheck_fn(void (*)(atomic_t *), fail_fn); \
|
|
\
|
|
asm volatile(LOCK_PREFIX " decl (%%rdi)\n" \
|
|
" jns 1f \n" \
|
|
" call " #fail_fn "\n" \
|
|
"1:" \
|
|
: "=D" (dummy) \
|
|
: "D" (v) \
|
|
: "rax", "rsi", "rdx", "rcx", \
|
|
"r8", "r9", "r10", "r11", "memory"); \
|
|
} while (0)
|
|
#endif
|
|
|
|
/**
|
|
* __mutex_fastpath_lock_retval - try to take the lock by moving the count
|
|
* from 1 to a 0 value
|
|
* @count: pointer of type atomic_t
|
|
*
|
|
* Change the count from 1 to a value lower than 1. This function returns 0
|
|
* if the fastpath succeeds, or -1 otherwise.
|
|
*/
|
|
static inline int __mutex_fastpath_lock_retval(atomic_t *count)
|
|
{
|
|
if (unlikely(atomic_dec_return(count) < 0))
|
|
return -1;
|
|
else
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* __mutex_fastpath_unlock - increment and call function if nonpositive
|
|
* @v: pointer of type atomic_t
|
|
* @fail_fn: function to call if the result is nonpositive
|
|
*
|
|
* Atomically increments @v and calls <fail_fn> if the result is nonpositive.
|
|
*/
|
|
#ifdef CC_HAVE_ASM_GOTO
|
|
static inline void __mutex_fastpath_unlock(atomic_t *v,
|
|
void (*fail_fn)(atomic_t *))
|
|
{
|
|
asm_volatile_goto(LOCK_PREFIX " incl %0\n"
|
|
" jg %l[exit]\n"
|
|
: : "m" (v->counter)
|
|
: "memory", "cc"
|
|
: exit);
|
|
fail_fn(v);
|
|
exit:
|
|
return;
|
|
}
|
|
#else
|
|
#define __mutex_fastpath_unlock(v, fail_fn) \
|
|
do { \
|
|
unsigned long dummy; \
|
|
\
|
|
typecheck(atomic_t *, v); \
|
|
typecheck_fn(void (*)(atomic_t *), fail_fn); \
|
|
\
|
|
asm volatile(LOCK_PREFIX " incl (%%rdi)\n" \
|
|
" jg 1f\n" \
|
|
" call " #fail_fn "\n" \
|
|
"1:" \
|
|
: "=D" (dummy) \
|
|
: "D" (v) \
|
|
: "rax", "rsi", "rdx", "rcx", \
|
|
"r8", "r9", "r10", "r11", "memory"); \
|
|
} while (0)
|
|
#endif
|
|
|
|
#define __mutex_slowpath_needs_to_unlock() 1
|
|
|
|
/**
|
|
* __mutex_fastpath_trylock - try to acquire the mutex, without waiting
|
|
*
|
|
* @count: pointer of type atomic_t
|
|
* @fail_fn: fallback function
|
|
*
|
|
* Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
|
|
* if it wasn't 1 originally. [the fallback function is never used on
|
|
* x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
|
|
*/
|
|
static inline int __mutex_fastpath_trylock(atomic_t *count,
|
|
int (*fail_fn)(atomic_t *))
|
|
{
|
|
if (likely(atomic_read(count) == 1 && atomic_cmpxchg(count, 1, 0) == 1))
|
|
return 1;
|
|
|
|
return 0;
|
|
}
|
|
|
|
#endif /* _ASM_X86_MUTEX_64_H */
|