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From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	mingo@kernel.org, jiangshanlai@gmail.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 5/8] doc: Update RCU requirements RCU_INIT_POINTER() description
Date: Tue,  5 Jan 2021 16:54:04 -0800
Message-ID: <20210106005407.12295-5-paulmck@kernel.org> (raw)
In-Reply-To: <20210106005334.GA12159@paulmck-ThinkPad-P72>

From: "Paul E. McKenney" <paulmck@kernel.org>

Back in the day, RCU_INIT_POINTER() was the only way to avoid
memory-barrier instructions while storing NULL to an RCU-protected
pointer.  Fortunately, in 2016, rcu_assign_pointer() started checking for
compile-time NULL pointers and omitting the memory-barrier instructions in
that case.  Unfortunately, RCU's Requirements.rst document was not updated
accordingly.  This commit therefore at long last carries out that update.

Fixes: 3a37f7275cda ("rcu: No ordering for rcu_assign_pointer() of NULL")
Link: https://lore.kernel.org/lkml/20201209230755.GV7338@casper.infradead.org/
Reported-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
 Documentation/RCU/Design/Requirements/Requirements.rst | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index f32f8fa..65c7839 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -1668,8 +1668,7 @@ against mishaps and misuse:
    this purpose.
 #. It is not necessary to use rcu_assign_pointer() when creating
    linked structures that are to be published via a single external
-   pointer. The RCU_INIT_POINTER() macro is provided for this task
-   and also for assigning ``NULL`` pointers at runtime.
+   pointer. The RCU_INIT_POINTER() macro is provided for this task.
 This not a hard-and-fast list: RCU's diagnostic capabilities will
 continue to be guided by the number and type of usage bugs found in

  parent reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-06  0:53 [PATCH tip/core/rcu 0/8] Documentation updates for v5.12 Paul E. McKenney
2021-01-06  0:54 ` [PATCH tip/core/rcu 1/8] docs: Remove redundant "``" from Requirements.rst paulmck
2021-01-06  0:54 ` [PATCH tip/core/rcu 2/8] doc: Remove obsolete RCU-bh and RCU-sched update-side API members paulmck
2021-01-06  0:54 ` [PATCH tip/core/rcu 3/8] list: Fix a typo at the kernel-doc markup paulmck
2021-01-06  0:54 ` [PATCH tip/core/rcu 4/8] docs: Fix typos and drop/fix dead links in RCU documentation paulmck
2021-01-06  0:54 ` paulmck [this message]
2021-01-06  0:54 ` [PATCH tip/core/rcu 6/8] doc: Remove obsolete rcutree.rcu_idle_lazy_gp_delay boot parameter paulmck
2021-01-06  0:54 ` [PATCH tip/core/rcu 7/8] doc: Update RCU's requirements page about the PREEMPT_RT wiki paulmck
2021-01-06  0:54 ` [PATCH tip/core/rcu 8/8] doc: Use CONFIG_PREEMPTION paulmck

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