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doc: Update rcu_access_pointer() advice in rcu_dereference.rst

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This commit updates the rcu_access_pointer() advice, noting that its
return value should not be assigned to a local variable, and also noting
that there is little point in using rcu_access_pointer() within an RCU
read-side critical section.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-08-04 11:23:19 -07:00
parent ca8a439e46
commit 022d1b356c
1 changed files with 10 additions and 4 deletions
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14
Documentation/RCU/rcu_dereference.rst
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@ -128,10 +128,16 @@ Follow these rules to keep your RCU code working properly:
This sort of comparison occurs frequently when scanning
RCU-protected circular linked lists.
Note that if checks for being within an RCU read-side
critical section are not required and the pointer is never
dereferenced, rcu_access_pointer() should be used in place
of rcu_dereference().
Note that if the pointer comparison is done outside
of an RCU read-side critical section, and the pointer
is never dereferenced, rcu_access_pointer() should be
used in place of rcu_dereference(). In most cases,
it is best to avoid accidental dereferences by testing
the rcu_access_pointer() return value directly, without
assigning it to a variable.
Within an RCU read-side critical section, there is little
reason to use rcu_access_pointer().
- The comparison is against a pointer that references memory
that was initialized "a long time ago." The reason