diff options
| author | Paul E. McKenney <paulmck@us.ibm.com> | 2005-09-10 00:26:24 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-09-10 10:06:24 -0700 |
| commit | dd81eca83c8300c95d8a1eaf0d38f56513711535 (patch) | |
| tree | a1cb1aee24b703b86f7197cfe4f379529a683c5a /Documentation/RCU/checklist.txt | |
| parent | 12c62c2e9abf8da804fe1def1f5bb44d023f569f (diff) | |
[PATCH] Yet another RCU documentation update
Update RCU documentation based on discussions and review of RCU-based tree
patches. Add an introductory whatisRCU.txt file.
Signed-off-by: <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation/RCU/checklist.txt')
| -rw-r--r-- | Documentation/RCU/checklist.txt | 23 |
1 files changed, 12 insertions, 11 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index 8f3fb77c9cd3..e118a7c1a092 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -43,6 +43,10 @@ over a rather long period of time, but improvements are always welcome! rcu_read_lock_bh()) in the read-side critical sections, and are also an excellent aid to readability. + As a rough rule of thumb, any dereference of an RCU-protected + pointer must be covered by rcu_read_lock() or rcu_read_lock_bh() + or by the appropriate update-side lock. + 3. Does the update code tolerate concurrent accesses? The whole point of RCU is to permit readers to run without @@ -90,7 +94,11 @@ over a rather long period of time, but improvements are always welcome! The rcu_dereference() primitive is used by the various "_rcu()" list-traversal primitives, such as the - list_for_each_entry_rcu(). + list_for_each_entry_rcu(). Note that it is perfectly + legal (if redundant) for update-side code to use + rcu_dereference() and the "_rcu()" list-traversal + primitives. This is particularly useful in code + that is common to readers and updaters. b. If the list macros are being used, the list_add_tail_rcu() and list_add_rcu() primitives must be used in order @@ -150,16 +158,9 @@ over a rather long period of time, but improvements are always welcome! Use of the _rcu() list-traversal primitives outside of an RCU read-side critical section causes no harm other than - a slight performance degradation on Alpha CPUs and some - confusion on the part of people trying to read the code. - - Another way of thinking of this is "If you are holding the - lock that prevents the data structure from changing, why do - you also need RCU-based protection?" That said, there may - well be situations where use of the _rcu() list-traversal - primitives while the update-side lock is held results in - simpler and more maintainable code. The jury is still out - on this question. + a slight performance degradation on Alpha CPUs. It can + also be quite helpful in reducing code bloat when common + code is shared between readers and updaters. 10. Conversely, if you are in an RCU read-side critical section, you -must- use the "_rcu()" variants of the list macros. |