Messages in this thread Patch in this message |  | | Date | Tue, 14 Jan 2014 10:28:23 +0800 | From | Daniel J Blueman <> | Subject | Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock() |
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On 14/01/2014 00:41, Waiman Long wrote: > On 01/12/2014 09:47 PM, Daniel J Blueman wrote: >> On Thursday, 9 January 2014 01:10:03 UTC+8, Waiman Long wrote: >> > This patch modifies the queue_write_unlock() function to use the >> > new smp_store_release() function in another pending patch. It also >> > removes the temporary implementation of smp_load_acquire() and >> > smp_store_release() function in qrwlock.c. >> > >> > This patch should only be merged if PeterZ's linux-arch patch patch >> > was merged. >> > >> > Signed-off-by: Waiman Long <Waiman.Long@hp.com> >> > Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> >> > --- >> > include/asm-generic/qrwlock.h | 4 +--- >> > kernel/locking/qrwlock.c | 34 >> ---------------------------------- >> > 2 files changed, 1 insertions(+), 37 deletions(-) >> > >> > diff --git a/include/asm-generic/qrwlock.h >> b/include/asm-generic/qrwlock.h >> > index 2b9a7b4..4d4bd04 100644 >> > --- a/include/asm-generic/qrwlock.h >> > +++ b/include/asm-generic/qrwlock.h >> > @@ -179,9 +179,7 @@ static inline void queue_write_unlock(struct >> qrwlock *lock) >> > /* >> > * Make sure that none of the critical section will be leaked out. >> > */ >> > - smp_mb__before_clear_bit(); >> > - ACCESS_ONCE(lock->cnts.writer) = 0; >> > - smp_mb__after_clear_bit(); >> > + smp_store_release(&lock->cnts.writer, 0) >> >> This will fail compilation, so probably needs further testing with >> Peter's load_acquire/store_release barrier patches. >> > > Peter, > > I found out that the build failure was caused by the fact that the > __native_word() macro (used internally by compiletime_assert_atomic()) > allows only a size of 4 or 8 for x86-64. The data type that I used is a > byte. Is there a reason why byte and short are not considered native?
It seems likely it was implemented like that since there was no existing need; long can be relied on as the largest native type, so this should suffice and works here:
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index fe7a686..dac91d7 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -299,8 +299,8 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); #endif
/* Is this type a native word size -- useful for atomic operations */ -#ifndef __native_word -# define __native_word(t) (sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long)) +#ifndef __native_type +# define __native_type(t) (sizeof(t) <= sizeof(long)) #endif
/* Compile time object size, -1 for unknown */ @@ -343,8 +343,8 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
#define compiletime_assert_atomic_type(t) \ - compiletime_assert(__native_word(t), \ - "Need native word sized stores/loads for atomicity.") + compiletime_assert(__native_type(t), \ + "Need native sized stores/loads for atomicity.")
/* * Prevent the compiler from merging or refetching accesses. The compiler Signed-off-by: Daniel J Blueman <daniel@numascale.com> -- Daniel J Blueman Principal Software Engineer, Numascale
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