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rcu: Describe listRCU read-side guarantees 

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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9
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. that all of the required memory ordering is provided by the list macros.
This document describes several list-based RCU use cases. 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 Example 1: Read-mostly list: Deferred Destruction
------------------------------------------------- -------------------------------------------------