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authorJoel Fernandes (Google) <joel@joelfernandes.org>2023-08-04 19:27:45 +0300
committerPaul E. McKenney <paulmck@kernel.org>2023-10-09 19:40:53 +0300
commit1566bf4b13daa66e3de6fdbc77ee3995df5a9064 (patch)
tree00aa5232c0dc62d326ee85ce4eb0f20c1465b9cc /Documentation/memory-barriers.txt
parent0bb80ecc33a8fb5a682236443c1e740d5c917d1d (diff)
downloadlinux-1566bf4b13daa66e3de6fdbc77ee3995df5a9064.tar.xz
docs: memory-barriers: Add note on compiler transformation and address deps
The compiler has the ability to cause misordering by destroying address-dependency barriers if comparison operations are used. Add a note about this to memory-barriers.txt in the beginning of both the historical address-dependency sections and point to rcu-dereference.rst for more information. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Will Deacon <will@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: David Howells <dhowells@redhat.com> Cc: Jade Alglave <j.alglave@ucl.ac.uk> Cc: Luc Maranget <luc.maranget@inria.fr> Cc: Akira Yokosawa <akiyks@gmail.com> Cc: Daniel Lustig <dlustig@nvidia.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Jonathan Corbet <corbet@lwn.net> Reviewed-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'Documentation/memory-barriers.txt')
-rw-r--r--Documentation/memory-barriers.txt7
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diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 06e14efd8662..d414e145f912 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -396,6 +396,10 @@ Memory barriers come in four basic varieties:
(2) Address-dependency barriers (historical).
+ [!] This section is marked as HISTORICAL: For more up-to-date
+ information, including how compiler transformations related to pointer
+ comparisons can sometimes cause problems, see
+ Documentation/RCU/rcu_dereference.rst.
An address-dependency barrier is a weaker form of read barrier. In the
case where two loads are performed such that the second depends on the
@@ -556,6 +560,9 @@ There are certain things that the Linux kernel memory barriers do not guarantee:
ADDRESS-DEPENDENCY BARRIERS (HISTORICAL)
----------------------------------------
+[!] This section is marked as HISTORICAL: For more up-to-date information,
+including how compiler transformations related to pointer comparisons can
+sometimes cause problems, see Documentation/RCU/rcu_dereference.rst.
As of v4.15 of the Linux kernel, an smp_mb() was added to READ_ONCE() for
DEC Alpha, which means that about the only people who need to pay attention