From 0612ea00a010e36fde61e7b7649a1105b0ef1080 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 10 Mar 2009 12:55:57 -0700 Subject: [PATCH] rcu: documentation 1Q09 update Update the RCU documentation to call out the need for callers of primitives like call_rcu() and synchronize_rcu() to prevent subsequent RCU readers from hazard. Signed-off-by: Paul E. McKenney Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/RCU/checklist.txt | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index 6e253407b3dc..accfe2f5247d 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -298,3 +298,15 @@ over a rather long period of time, but improvements are always welcome! Note that, rcu_assign_pointer() and rcu_dereference() relate to SRCU just as they do to other forms of RCU. + +15. The whole point of call_rcu(), synchronize_rcu(), and friends + is to wait until all pre-existing readers have finished before + carrying out some otherwise-destructive operation. It is + therefore critically important to -first- remove any path + that readers can follow that could be affected by the + destructive operation, and -only- -then- invoke call_rcu(), + synchronize_rcu(), or friends. + + Because these primitives only wait for pre-existing readers, + it is the caller's responsibility to guarantee safety to + any subsequent readers.