similar to: [PATCH 00/18] Allow architectures to override __READ_ONCE()

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

On Fri, Jul 10, 2020 at 05:51:46PM +0100, Will Deacon wrote: > In preparation for allowing architectures to define their own > implementation of the READ_ONCE() macro, move the generic > {READ,WRITE}_ONCE() definitions out of the unwieldy 'linux/compiler.h' > file and into a new 'rwonce.h' header under 'asm-generic'. > > Acked-by: Paul E. McKenney

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

On Tue, Jun 30, 2020 at 7:37 PM Will Deacon <will at kernel.org> wrote: > > In preparation for allowing architectures to define their own > implementation of the READ_ONCE() macro, move the generic > {READ,WRITE}_ONCE() definitions out of the unwieldy 'linux/compiler.h' > file and into a new 'rwonce.h' header under 'asm-generic'. > > Acked-by:

The patch below fixes the recent UML compilation failure in -rc5-mm1 without making the UML build reach further into the i386 headers. It splits the i386 ptrace.h and system.h into UML-usable and UML-unusable pieces. The string "abi" is in there because I did ptrace.h first, and that involves separating the ptrace ABI stuff from everything else (if pt_regs is not considered part of

The patch below fixes the recent UML compilation failure in -rc5-mm1 without making the UML build reach further into the i386 headers. It splits the i386 ptrace.h and system.h into UML-usable and UML-unusable pieces. The string "abi" is in there because I did ptrace.h first, and that involves separating the ptrace ABI stuff from everything else (if pt_regs is not considered part of

In preparation for allowing architectures to define their own implementation of the READ_ONCE() macro, move the generic {READ,WRITE}_ONCE() definitions out of the unwieldy 'linux/compiler.h' file and into a new 'rwonce.h' header under 'asm-generic'. Acked-by: Paul E. McKenney <paulmck at kernel.org> Signed-off-by: Will Deacon <will at kernel.org> ---

On Fri, Jul 10, 2020 at 9:52 AM Will Deacon <will at kernel.org> wrote: > > Now that 'smp_read_barrier_depends()' has gone the way of the Norwegian > Blue, drop the inclusion of <asm/barrier.h> in 'asm-generic/rwonce.h'. > > This requires fixups to some architecture vdso headers which were > previously relying on 'asm/barrier.h' coming in via

This changes the pv ops code generation to more closely match reality. For example, instead of: callq *0xffffffff81e3a400 (pv_irq_ops.save_fl) vmlinux will now show: pushfq pop %rax nop nop nop nop nop which is what the runtime version of the code will show in most cases. This idea was suggested by Andy Lutomirski. The benefits are: - For the most common runtime cases

This changes the pv ops code generation to more closely match reality. For example, instead of: callq *0xffffffff81e3a400 (pv_irq_ops.save_fl) vmlinux will now show: pushfq pop %rax nop nop nop nop nop which is what the runtime version of the code will show in most cases. This idea was suggested by Andy Lutomirski. The benefits are: - For the most common runtime cases

Now that 'smp_read_barrier_depends()' has gone the way of the Norwegian Blue, drop the inclusion of <asm/barrier.h> in 'asm-generic/rwonce.h'. This requires fixups to some architecture vdso headers which were previously relying on 'asm/barrier.h' coming in via 'linux/compiler.h'. Signed-off-by: Will Deacon <will at kernel.org> ---

On Tue, Jun 30, 2020 at 06:37:20PM +0100, Will Deacon wrote: > Rather then relying on the core code to use smp_read_barrier_depends() > as part of the READ_ONCE() definition, instead override __READ_ONCE() > in the Alpha code so that it is treated the same way as > smp_load_acquire(). > > Acked-by: Paul E. McKenney <paulmck at kernel.org> > Signed-off-by: Will Deacon

On Tue, Jun 30, 2020 at 06:37:20PM +0100, Will Deacon wrote: > Rather then relying on the core code to use smp_read_barrier_depends() > as part of the READ_ONCE() definition, instead override __READ_ONCE() > in the Alpha code so that it is treated the same way as > smp_load_acquire(). > > Acked-by: Paul E. McKenney <paulmck at kernel.org> > Signed-off-by: Will Deacon

When building with LTO, there is an increased risk of the compiler converting an address dependency headed by a READ_ONCE() invocation into a control dependency and consequently allowing for harmful reordering by the CPU. Ensure that such transformations are harmless by overriding the generic READ_ONCE() definition with one that provides acquire semantics when building with LTO. Signed-off-by:

In preparation for allowing architectures to define their own implementation of the READ_ONCE() macro, move the generic {READ,WRITE}_ONCE() definitions out of the unwieldy 'linux/compiler.h' file and into a new 'rwonce.h' header under 'asm-generic'. Acked-by: Paul E. McKenney <paulmck at kernel.org> Signed-off-by: Will Deacon <will at kernel.org> ---

The meat and potatoes of READ_ONCE() is defined by the __READ_ONCE() macro, which uses a volatile casts in an attempt to avoid tearing of byte, halfword, word and double-word accesses. Allow this to be overridden by the architecture code in the case that things like memory barriers are also required. Acked-by: Paul E. McKenney <paulmck at kernel.org> Signed-off-by: Will Deacon <will at

On Fri, Nov 8, 2019 at 6:01 PM Will Deacon <will at kernel.org> wrote: > > In preparation for allowing architectures to define their own > implementation of the 'READ_ONCE()' macro, move the generic > '{READ,WRITE}_ONCE()' definitions out of the unwieldy 'linux/compiler.h' > and into a new 'rwonce.h' header under 'asm-generic'. Adding

On Fri, Nov 8, 2019 at 6:01 PM Will Deacon <will at kernel.org> wrote: > > In preparation for allowing architectures to define their own > implementation of the 'READ_ONCE()' macro, move the generic > '{READ,WRITE}_ONCE()' definitions out of the unwieldy 'linux/compiler.h' > and into a new 'rwonce.h' header under 'asm-generic'. Adding

Hi Paul, On Mon, Jan 18, 2016 at 07:46:29AM -0800, Paul E. McKenney wrote: > On Mon, Jan 18, 2016 at 04:19:29PM +0800, Herbert Xu wrote: > > Paul E. McKenney <paulmck at linux.vnet.ibm.com> wrote: > > > > > > You could use SYNC_ACQUIRE() to implement read_barrier_depends() and > > > smp_read_barrier_depends(), but SYNC_RMB probably does not suffice. >