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...ion on "Multicopy atomicity" > for more information. > > > + > + > In summary: > > (*) Control dependencies can order prior loads against later stores. > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.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. > */ &g...

...ion on "Multicopy atomicity" > for more information. > > > + > + > In summary: > > (*) Control dependencies can order prior loads against later stores. > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.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. > */ &g...

Hi Joel, On Thu, Jul 02, 2020 at 10:43:55AM -0400, Joel Fernandes wrote: > On Tue, Jun 30, 2020 at 1:38 PM Will Deacon <will at kernel.org> wrote: > > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h > > index 92ec486a4f9e..2ecd068d91d1 100644 > > --- a/arch/alpha/include/asm/barrier.h > > +++ b/arch/alpha/include/asm/barrier.h > > - * For example, the following code would force ordering (the initial > > - * value of "a" is zero, "b" is one, and "p" is "&...

...clude/asm/barrier.h | 61 ++++---------------------------- arch/alpha/include/asm/rwonce.h | 19 ++++++++++ 2 files changed, 26 insertions(+), 54 deletions(-) create mode 100644 arch/alpha/include/asm/rwonce.h diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h index 92ec486a4f9e..2ecd068d91d1 100644 --- a/arch/alpha/include/asm/barrier.h +++ b/arch/alpha/include/asm/barrier.h @@ -2,64 +2,17 @@ #ifndef __BARRIER_H #define __BARRIER_H -#include <asm/compiler.h> - #define mb() __asm__ __volatile__("mb": : :"memory") #define rmb() __asm__ __vola...

...-875,6 +893,8 @@ to the CPU containing it. See the section on "Multicopy atomicity" for more information. + + In summary: (*) Control dependencies can order prior loads against later stores. diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.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_DE...

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

...t;Multicopy atomicity" > > for more information. > > + > > + > > In summary: > > (*) Control dependencies can order prior loads against later stores. > > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.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 de...

...--------------------------- > arch/alpha/include/asm/rwonce.h | 19 ++++++++++ > 2 files changed, 26 insertions(+), 54 deletions(-) > create mode 100644 arch/alpha/include/asm/rwonce.h > > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h > index 92ec486a4f9e..2ecd068d91d1 100644 > --- a/arch/alpha/include/asm/barrier.h > +++ b/arch/alpha/include/asm/barrier.h > @@ -2,64 +2,17 @@ > #ifndef __BARRIER_H > #define __BARRIER_H > > -#include <asm/compiler.h> > - > #define mb() __asm__ __volatile__("mb": : :&quo...

...--------------------------- > arch/alpha/include/asm/rwonce.h | 19 ++++++++++ > 2 files changed, 26 insertions(+), 54 deletions(-) > create mode 100644 arch/alpha/include/asm/rwonce.h > > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h > index 92ec486a4f9e..2ecd068d91d1 100644 > --- a/arch/alpha/include/asm/barrier.h > +++ b/arch/alpha/include/asm/barrier.h > @@ -2,64 +2,17 @@ > #ifndef __BARRIER_H > #define __BARRIER_H > > -#include <asm/compiler.h> > - > #define mb() __asm__ __volatile__("mb": : :&quo...

Hi everyone, This is the long-awaited version two of the patches I previously posted in November last year: https://lore.kernel.org/lkml/20191108170120.22331-1-will at kernel.org/ I ended up parking the series while the READ_ONCE() implementation was being overhauled, but with that merged during the recent merge window and LTO patches being posted again [1], it was time for a refresh. The

Hi everyone, This is the long-awaited version two of the patches I previously posted in November last year: https://lore.kernel.org/lkml/20191108170120.22331-1-will at kernel.org/ I ended up parking the series while the READ_ONCE() implementation was being overhauled, but with that merged during the recent merge window and LTO patches being posted again [1], it was time for a refresh. The

Hi all, Although [smp_]read_barrier_depends() became part of READ_ONCE() in commit 76ebbe78f739 ("locking/barriers: Add implicit smp_read_barrier_depends() to READ_ONCE()"), it still limps on in the Linux memory model with the sinister hope of attracting innocent new users so that it becomes impossible to remove altogether. Let's strike before it's too late: there's only

Hi all, This is version three of the patches I previously posted here: v1: https://lore.kernel.org/lkml/20191108170120.22331-1-will at kernel.org/ v2: https://lore.kernel.org/r/20200630173734.14057-1-will at kernel.org Changes since v2 include: * Actually add the barrier in READ_ONCE() for Alpha! * Implement Alpha's smp_load_acquire() using __READ_ONCE(), rather than the other