search for: arch_needs_read_barrier_depend

...1b 100644 > --- a/arch/alpha/include/asm/barrier.h > +++ b/arch/alpha/include/asm/barrier.h > @@ -59,6 +59,7 @@ > * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb() > * in cases like this where there are no data dependencies. > */ > +#define ARCH_NEEDS_READ_BARRIER_DEPENDS 1 > #define read_barrier_depends() __asm__ __volatile__("mb": : :"memory") > > #ifdef CONFIG_SMP > diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h > index 2cafdbb9ae4c..fa2e2ef72b68 100644 > --- a/include/asm-generic/barrier.h...

...1b 100644 > --- a/arch/alpha/include/asm/barrier.h > +++ b/arch/alpha/include/asm/barrier.h > @@ -59,6 +59,7 @@ > * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb() > * in cases like this where there are no data dependencies. > */ > +#define ARCH_NEEDS_READ_BARRIER_DEPENDS 1 > #define read_barrier_depends() __asm__ __volatile__("mb": : :"memory") > > #ifdef CONFIG_SMP > diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h > index 2cafdbb9ae4c..fa2e2ef72b68 100644 > --- a/include/asm-generic/barrier.h...

...rrier.h index 92ec486a4f9e..b4934e8c551b 100644 --- a/arch/alpha/include/asm/barrier.h +++ b/arch/alpha/include/asm/barrier.h @@ -59,6 +59,7 @@ * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb() * in cases like this where there are no data dependencies. */ +#define ARCH_NEEDS_READ_BARRIER_DEPENDS 1 #define read_barrier_depends() __asm__ __volatile__("mb": : :"memory") #ifdef CONFIG_SMP diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index 2cafdbb9ae4c..fa2e2ef72b68 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrie...

So as explained in Documentation/memory-barriers.txt e.g. a load followed by a store require a full memory barrier, to avoid store being ordered before the load. Similarly load-load requires a read memory barrier. Thinking about it, we can actually create a data dependency by mixing the first loaded value into the pointer being accessed. This adds an API for this and uses it in virtio. Written

...a/include/asm/barrier.h > > +++ b/arch/alpha/include/asm/barrier.h > > @@ -59,6 +59,7 @@ > > * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb() > > * in cases like this where there are no data dependencies. > > */ > > +#define ARCH_NEEDS_READ_BARRIER_DEPENDS 1 > > #define read_barrier_depends() __asm__ __volatile__("mb": : :"memory") > > #ifdef CONFIG_SMP > > diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h > > index 2cafdbb9ae4c..fa2e2ef72b68 100644 > > --- a/include/asm-...