On Sun, 29 May 2011 23:19:28 -0400
Mike Frysinger <vapier@xxxxxxxxxx> wrote:
> To make these guys work on SMP systems, we just need to sprinkle a few
> barriers around.
>
> Signed-off-by: Mike Frysinger <vapier@xxxxxxxxxx>
> ---
> note: this is what the Blackfin SMP port is using, but it doesn't seem
> like other SMP ports are ... so I wonder if we're just trying too hard
> and these barriers aren't actually necessary ?
>
> include/asm-generic/mutex-dec.h | 8 +++++++-
> 1 files changed, 7 insertions(+), 1 deletions(-)
>
> diff --git a/include/asm-generic/mutex-dec.h b/include/asm-generic/mutex-dec.h
> index f104af7..e746c3c 100644
> --- a/include/asm-generic/mutex-dec.h
> +++ b/include/asm-generic/mutex-dec.h
> @@ -22,6 +22,8 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
> {
> if (unlikely(atomic_dec_return(count) < 0))
> fail_fn(count);
> + else
> + smp_mb();
> }
>
> /**
> @@ -39,6 +41,7 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
> {
> if (unlikely(atomic_dec_return(count) < 0))
> return fail_fn(count);
> + smp_mb();
> return 0;
> }
>
> @@ -58,6 +61,7 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
> static inline void
> __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
> {
> + smp_mb();
> if (unlikely(atomic_inc_return(count) <= 0))
> fail_fn(count);
> }
> @@ -82,8 +86,10 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
> static inline int
> __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
> {
> - if (likely(atomic_cmpxchg(count, 1, 0) == 1))
> + if (likely(atomic_cmpxchg(count, 1, 0) == 1)) {
> + smp_mb();
> return 1;
> + }
> return 0;
> }
This patch basically reverts Nick's a8ddac7e53e89cb ("mutex: speed up
generic mutex implementations"). What's up with that?
I could try to review this patch but I'm pathetic with barriers. Help.
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