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| author | Joel Fernandes (Google) <joel@joelfernandes.org> | 2023-08-04 19:27:45 +0300 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2023-10-09 19:40:53 +0300 |
| commit | 1566bf4b13daa66e3de6fdbc77ee3995df5a9064 (patch) | |
| tree | 00aa5232c0dc62d326ee85ce4eb0f20c1465b9cc /Documentation/memory-barriers.txt | |
| parent | 0bb80ecc33a8fb5a682236443c1e740d5c917d1d (diff) | |
| download | linux-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.txt | 7 |
1 files changed, 7 insertions, 0 deletions
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 |