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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-02-22 17:04:57 -0800
committerIngo Molnar <mingo@elte.hu>2010-02-25 10:34:53 +0100
commitc598a070bc581aea8a518b460dae8c0cf8e74344 (patch)
treea74f0323a7432ff836901ca301ca11870d73f940 /Documentation/RCU/checklist.txt
parente7b0a61b7929632d36cf052d9e2820ef0a9c1bfe (diff)
downloadlinux-linaro-stable-c598a070bc581aea8a518b460dae8c0cf8e74344.tar.gz
rcu: Documentation update for CONFIG_PROVE_RCU
Adds a lockdep.txt file and updates checklist.txt and whatisRCU.txt to reflect the new lockdep-enabled capabilities of RCU. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-13-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'Documentation/RCU/checklist.txt')
-rw-r--r--Documentation/RCU/checklist.txt34
1 files changed, 20 insertions, 14 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 767cf06a4276..cbc180f90194 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -127,10 +127,14 @@ over a rather long period of time, but improvements are always welcome!
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. However, neither
- rcu_dereference() nor the "_rcu()" list-traversal
- primitives can substitute for a good concurrency design
- coordinating among multiple updaters.
+ is common to readers and updaters. However, lockdep
+ will complain if you access rcu_dereference() outside
+ of an RCU read-side critical section. See lockdep.txt
+ to learn what to do about this.
+
+ Of course, neither rcu_dereference() nor the "_rcu()"
+ list-traversal primitives can substitute for a good
+ concurrency design coordinating among multiple updaters.
b. If the list macros are being used, the list_add_tail_rcu()
and list_add_rcu() primitives must be used in order
@@ -249,7 +253,9 @@ over a rather long period of time, but improvements are always welcome!
must be protected by appropriate update-side locks. RCU
read-side critical sections are delimited by rcu_read_lock()
and rcu_read_unlock(), or by similar primitives such as
- rcu_read_lock_bh() and rcu_read_unlock_bh().
+ rcu_read_lock_bh() and rcu_read_unlock_bh(), in which case
+ the matching rcu_dereference() primitive must be used in order
+ to keep lockdep happy, in this case, rcu_dereference_bh().
The reason that it is permissible to use RCU list-traversal
primitives when the update-side lock is held is that doing so
@@ -302,15 +308,15 @@ over a rather long period of time, but improvements are always welcome!
not the case, a self-spawning RCU callback would prevent the
victim CPU from ever going offline.)
-14. SRCU (srcu_read_lock(), srcu_read_unlock(), synchronize_srcu(),
- and synchronize_srcu_expedited()) 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()), hence the "SRCU":
- "sleepable RCU". Please note that if you don't need to sleep
- in read-side critical sections, you should be using RCU rather
- than SRCU, because RCU is almost always faster and easier to
- use than is SRCU.
+14. SRCU (srcu_read_lock(), srcu_read_unlock(), srcu_dereference(),
+ synchronize_srcu(), and synchronize_srcu_expedited()) 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()), hence the
+ "SRCU": "sleepable RCU". Please note that if you don't need
+ to sleep in read-side critical sections, you should be using
+ RCU rather than SRCU, because RCU is almost always faster and
+ easier to use than is SRCU.
Also unlike other forms of RCU, explicit initialization
and cleanup is required via init_srcu_struct() and