Messages in this thread | | | Date | Thu, 15 Feb 2018 18:08:47 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 3/5] asm-generic/bitops/atomic.h: Rewrite using atomic_fetch_* |
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On Thu, Feb 15, 2018 at 03:29:33PM +0000, Will Deacon wrote: > +static inline void set_bit(unsigned int nr, volatile unsigned long *p) > +{ > + p += BIT_WORD(nr); > + atomic_long_fetch_or_relaxed(BIT_MASK(nr), (atomic_long_t *)p); > +} > > +static inline void clear_bit(unsigned int nr, volatile unsigned long *p) > +{ > + p += BIT_WORD(nr); > + atomic_long_fetch_andnot_relaxed(BIT_MASK(nr), (atomic_long_t *)p); > +} > > +static inline void change_bit(unsigned int nr, volatile unsigned long *p) > +{ > + p += BIT_WORD(nr); > + atomic_long_fetch_xor_relaxed(BIT_MASK(nr), (atomic_long_t *)p); > +} > > +static inline int test_and_set_bit(unsigned int nr, volatile unsigned long *p) > { > + long old; > unsigned long mask = BIT_MASK(nr); > > + p += BIT_WORD(nr); > + if (READ_ONCE(*p) & mask) > + return 1; > + > + old = atomic_long_fetch_or(mask, (atomic_long_t *)p); > + return !!(old & mask); > } > > +static inline int test_and_clear_bit(unsigned int nr, volatile unsigned long *p) > { > + long old; > unsigned long mask = BIT_MASK(nr); > > + p += BIT_WORD(nr); > + if (!(READ_ONCE(*p) & mask)) > + return 0; > + > + old = atomic_long_fetch_andnot(mask, (atomic_long_t *)p); > + return !!(old & mask); > } > > +static inline int test_and_change_bit(unsigned int nr, volatile unsigned long *p) > { > + long old; > unsigned long mask = BIT_MASK(nr); > > + p += BIT_WORD(nr); > + old = atomic_long_fetch_xor(mask, (atomic_long_t *)p); > + return !!(old & mask); > } > > +static inline int test_and_set_bit_lock(unsigned int nr, > + volatile unsigned long *p) > { > + long old; > unsigned long mask = BIT_MASK(nr); > > + p += BIT_WORD(nr); > + if (READ_ONCE(*p) & mask) > + return 1; > > + old = atomic_long_fetch_or_acquire(mask, (atomic_long_t *)p); > + return !!(old & mask); > } > > +static inline void clear_bit_unlock(unsigned int nr, volatile unsigned long *p) > { > + p += BIT_WORD(nr); > + atomic_long_fetch_andnot_release(BIT_MASK(nr), (atomic_long_t *)p); > +} > > +static inline void __clear_bit_unlock(unsigned int nr, > + volatile unsigned long *p) > +{ > + unsigned long old; > > + p += BIT_WORD(nr); > + old = READ_ONCE(*p); > + old &= ~BIT_MASK(nr); > + smp_store_release(p, old);
This should be atomic_set_release() I think, for the special case where atomics are implemented with spinlocks, see the 'fun' case in Documentation/atomic_t.txt.
> }
The only other comment is that I think it would be better if you use atomic_t instead of atomic_long_t. It would just mean changing BIT_WORD() and BIT_MASK().
The reason is that we generate a pretty sane set of atomic_t primitives as long as the architecture supplies cmpxchg, but atomic64 defaults to utter crap, even on 64bit platforms.
Otherwise this looks pretty neat.
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