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.l...@hp.com>
> Reviewed-by: Paul E. McKenney <paul...@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 <dan...@numascale.com>
--
Daniel J Blueman
Principal Software Engineer, Numascale
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