From: Paul E. McKenney Date: Mon, 16 Jul 2007 06:41:03 +0000 (-0700) Subject: Document the fact that RCU callbacks can run in parallel X-Git-Tag: v2.6.23-rc1~866 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ef48bd246124ccdef0e1fa5b03b62d69cbf71fa7;p=linux-2.6 Document the fact that RCU callbacks can run in parallel Add an item to the RCU documentation checklist noting that RCU callbacks can run in parallel. Signed-off-by: Paul E. McKenney Cc: Steven Rostedt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index f4dffadbcb..42b01bc2e1 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -222,7 +222,15 @@ over a rather long period of time, but improvements are always welcome! deadlock as soon as the RCU callback happens to interrupt that acquisition's critical section. -13. SRCU (srcu_read_lock(), srcu_read_unlock(), and synchronize_srcu()) +13. RCU callbacks can be and are executed in parallel. In many cases, + the callback code simply wrappers around kfree(), so that this + is not an issue (or, more accurately, to the extent that it is + an issue, the memory-allocator locking handles it). However, + if the callbacks do manipulate a shared data structure, they + must use whatever locking or other synchronization is required + to safely access and/or modify that data structure. + +14. SRCU (srcu_read_lock(), srcu_read_unlock(), and synchronize_srcu()) may only be invoked from process context. Unlike other forms of RCU, it -is- permissible to block in an SRCU read-side critical section (demarked by srcu_read_lock() and srcu_read_unlock()),