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...; architecture? I have a pile of powerpc-related litmus tests on my laptop, > but they probably aren't doing all that much good there. Yeah, or a version of them in C that we can 'compile'? > > commit 2cb4e83a1b5c89c8e39b8a64bd89269d05913e41 > Author: Paul E. McKenney <paulmck at linux.vnet.ibm.com> > Date: Fri Jan 15 09:30:42 2016 -0800 > > documentation: Distinguish between local and global transitivity > > The introduction of smp_load_acquire() and smp_store_release() had > the side effect of introducing a weaker notion of tran...

...; architecture? I have a pile of powerpc-related litmus tests on my laptop, > but they probably aren't doing all that much good there. Yeah, or a version of them in C that we can 'compile'? > > commit 2cb4e83a1b5c89c8e39b8a64bd89269d05913e41 > Author: Paul E. McKenney <paulmck at linux.vnet.ibm.com> > Date: Fri Jan 15 09:30:42 2016 -0800 > > documentation: Distinguish between local and global transitivity > > The introduction of smp_load_acquire() and smp_store_release() had > the side effect of introducing a weaker notion of tran...

...re architects. Yeah, this goes under the header: memory-barriers.txt is _NOT_ a specification (I seem to keep repeating this). > ------------------------------------------------------------------------ > > commit 955720966e216b00613fcf60188d507c103f0e80 > Author: Paul E. McKenney <paulmck at linux.vnet.ibm.com> > Date: Thu Jan 14 14:17:04 2016 -0800 > > documentation: Subsequent writes ordered by rcu_dereference() > > The current memory-barriers.txt does not address the possibility of > a write to a dereferenced pointer. This should be rare,...

...re architects. Yeah, this goes under the header: memory-barriers.txt is _NOT_ a specification (I seem to keep repeating this). > ------------------------------------------------------------------------ > > commit 955720966e216b00613fcf60188d507c103f0e80 > Author: Paul E. McKenney <paulmck at linux.vnet.ibm.com> > Date: Thu Jan 14 14:17:04 2016 -0800 > > documentation: Subsequent writes ordered by rcu_dereference() > > The current memory-barriers.txt does not address the possibility of > a write to a dereferenced pointer. This should be rare,...

Commit-ID: 3a5db0b108e0a40f08c2bcff6a675dbf632b91e0 Gitweb: https://git.kernel.org/tip/3a5db0b108e0a40f08c2bcff6a675dbf632b91e0 Author: Paul E. McKenney <paulmck at linux.vnet.ibm.com> AuthorDate: Mon, 27 Nov 2017 09:45:10 -0800 Committer: Paul E. McKenney <paulmck at linux.vnet.ibm.com> CommitDate: Tue, 5 Dec 2017 11:57:55 -0800 drivers/vhost: Remove now-redundant read_barrier_depends() Because READ_ONCE() now implies read_barrier_depends(), th...

Commit-ID: d05faa5f1ac50beef77b4ceba0e8e157d41146e2 Gitweb: https://git.kernel.org/tip/d05faa5f1ac50beef77b4ceba0e8e157d41146e2 Author: Paul E. McKenney <paulmck at linux.ibm.com> AuthorDate: Mon, 5 Nov 2018 17:14:53 -0800 Committer: Paul E. McKenney <paulmck at linux.ibm.com> CommitDate: Tue, 27 Nov 2018 09:21:37 -0800 drivers/vhost: Replace synchronize_rcu_bh() with synchronize_rcu() Now that synchronize_rcu() waits for bh-disable regions of c...

..., as discussed in the following thread: http://www.mail-archive.com/netdev@vger.kernel.org/msg54852.html Tested on x86_64 and ppc64, also compiled the four cases (NULL/non-NULL and const/non-const) with gcc version 4.1.2, and hand-checked the assembly output. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- rcupdate.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff -urpNa -X dontdiff linux-2.6.24-rc1-ego/include/linux/rcupdate.h linux-2.6.24-rc1-egoxu/include/linux/rcupdate.h --- linux-2.6.24-rc1-ego/include/linux/rcupdate.h 2007-11-06 15:30:02.00...

....kernel.org> > Cc: Andrew Morton <akpm at linux-foundation.org> > Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org> > Cc: Heiko Carstens <heiko.carstens at de.ibm.com> > Cc: Linus Torvalds <torvalds at linux-foundation.org> > Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com> > Cc: Peter Zijlstra <peterz at infradead.org> > Cc: Thomas Gleixner <tglx at linutronix.de> > Cc: Tony Luck <tony.luck at intel.com> > Cc: dave at stgolabs.net > Link: http://lkml.kernel.org/r/1445975631-17047-3-git-send-email-dave at stgo...

....kernel.org> > Cc: Andrew Morton <akpm at linux-foundation.org> > Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org> > Cc: Heiko Carstens <heiko.carstens at de.ibm.com> > Cc: Linus Torvalds <torvalds at linux-foundation.org> > Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com> > Cc: Peter Zijlstra <peterz at infradead.org> > Cc: Thomas Gleixner <tglx at linutronix.de> > Cc: Tony Luck <tony.luck at intel.com> > Cc: dave at stgolabs.net > Link: http://lkml.kernel.org/r/1445975631-17047-3-git-send-email-dave at stgo...

...chitectures 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> > --- > include/asm-generic/Kbuild | 1 + > include/asm-generic/rwonce.h | 91 ++++++++++++++++++++++++++++++++++++ > include/linux/compiler.h | 83 +------------------------------- Very nice, this has...

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. > The reason for this is that smp_read_barrier_depends() must order the > pointer load against any subsequen...

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. > The reason for this is that smp_read_barrier_depends() must order the > pointer load against any subsequen...

On Thu, Jan 14, 2016 at 01:29:13PM -0800, Paul E. McKenney wrote: > So smp_mb() provides transitivity, as do pairs of smp_store_release() > and smp_read_acquire(), But they provide different grades of transitivity, which is where all the confusion lays. smp_mb() is strongly/globally transitive, all CPUs will agree on the order. Whereas the RCpc release+acquire is weakly so, only the two

On Thu, Jan 14, 2016 at 01:29:13PM -0800, Paul E. McKenney wrote: > So smp_mb() provides transitivity, as do pairs of smp_store_release() > and smp_read_acquire(), But they provide different grades of transitivity, which is where all the confusion lays. smp_mb() is strongly/globally transitive, all CPUs will agree on the order. Whereas the RCpc release+acquire is weakly so, only the two

...t > +++ b/Documentation/memory-barriers.txt > @@ -1,3 +1,4 @@ > + > ============================ > LINUX KERNEL MEMORY BARRIERS > ============================ > @@ -5,6 +6,22 @@ > By: David Howells <dhowells at redhat.com> > Paul E. McKenney <paulmck at linux.vnet.ibm.com> > > +========== > +DISCLAIMER > +========== > + > +This document is not a specification; it is intentionally (for the sake of > +brevity) and unintentionally (due to being human) incomplete. This document is > +meant as a guide to using the variou...

...t > +++ b/Documentation/memory-barriers.txt > @@ -1,3 +1,4 @@ > + > ============================ > LINUX KERNEL MEMORY BARRIERS > ============================ > @@ -5,6 +6,22 @@ > By: David Howells <dhowells at redhat.com> > Paul E. McKenney <paulmck at linux.vnet.ibm.com> > > +========== > +DISCLAIMER > +========== > + > +This document is not a specification; it is intentionally (for the sake of > +brevity) and unintentionally (due to being human) incomplete. This document is > +meant as a guide to using the variou...

From: "Paul E. McKenney" <paulmck at linux.vnet.ibm.com> The sparse checking for rcu_assign_pointer() was recently upgraded to reject non-__kernel address spaces. This also rejects __rcu, which is almost always the right thing to do. However, the use in __br_mdb_del() is legitimate: They are assigning a pointer to an element...

On Feb 27, 2016 09:06, "Paul E. McKenney" <paulmck at linux.vnet.ibm.com> wrote: > > > But we do already have something very similar with signed integer > overflow. If the compiler can see a way to generate faster code that > does not handle the overflow case, then the semantics suddenly change > from twos-complement arithmeti...

Because READ_ONCE() now implies read_barrier_depends(), the read_barrier_depends() in next_desc() is now redundant. This commit therefore removes it and the related comments. Signed-off-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com> Cc: "Michael S. Tsirkin" <mst at redhat.com> Cc: Jason Wang <jasowang at redhat.com> Cc: <kvm at vger.kernel.org> Cc: <virtualization at lists.linux-foundation.org> Cc: <netdev at vger.kernel.org> --- drivers/vhost/vhost.c | 7 +----...

Because READ_ONCE() now implies read_barrier_depends(), the read_barrier_depends() in next_desc() is now redundant. This commit therefore removes it and the related comments. Signed-off-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com> Cc: "Michael S. Tsirkin" <mst at redhat.com> Cc: Jason Wang <jasowang at redhat.com> Cc: <kvm at vger.kernel.org> Cc: <virtualization at lists.linux-foundation.org> Cc: <netdev at vger.kernel.org> --- drivers/vhost/vhost.c | 7 +----...