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rcu: Describe listRCU read-side guarantees

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More explicitly state what is, and what is not guaranteed to those
who iterate a list while protected by RCU.

[ paulmck: Apply Joel Fernandes feedback. ]

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2023-08-22 21:04:02 +01:00 committed by Frederic Weisbecker
parent ebbb9d35fd
commit 082acfe39c
1 changed files with 9 additions and 0 deletions
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Documentation/RCU/listRCU.rst
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@ -8,6 +8,15 @@ One of the most common uses of RCU is protecting read-mostly linked lists
that all of the required memory ordering is provided by the list macros.
This document describes several list-based RCU use cases.
When iterating a list while holding the rcu_read_lock(), writers may
modify the list. The reader is guaranteed to see all of the elements
which were added to the list before they acquired the rcu_read_lock()
and are still on the list when they drop the rcu_read_unlock().
Elements which are added to, or removed from the list may or may not
be seen. If the writer calls list_replace_rcu(), the reader may see
either the old element or the new element; they will not see both,
nor will they see neither.
Example 1: Read-mostly list: Deferred Destruction
-------------------------------------------------