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doc: Update RCU requirements RCU_INIT_POINTER() description 

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: 3a37f7275c ("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>
This commit is contained in:
Paul E. McKenney 2020-12-09 16:54:41 -08:00
parent 9d3a04853f
commit d756c74e6f
1 changed files with 1 additions and 2 deletions
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Documentation/RCU/Design/Requirements/Requirements.rst
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@ -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