path: root/kernel/rcutree.h
diff options
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2009-11-02 13:52:28 -0800
committerIngo Molnar <mingo@elte.hu>2009-11-10 04:11:54 +0100
commitd09b62dfa336447c52a5ec9bb88adbc479b0f3b8 (patch)
tree70a002fed2e0471def01ea3c166137449cb1527d /kernel/rcutree.h
parent281d150c5f8892f158747594ab49ce2823fd8b8c (diff)
rcu: Fix synchronization for rcu_process_gp_end() uses of ->completed counter
Impose a clear locking design on the rcu_process_gp_end() function's use of the ->completed counter. This is done by creating a ->completed field in the rcu_node structure, which can safely be accessed under the protection of that structure's lock. Performance and scalability are maintained by using a form of double-checked locking, so that rcu_process_gp_end() only acquires the leaf rcu_node structure's ->lock if a grace period has recently ended. This fix reduces rcutorture failure rate by at least two orders of magnitude under heavy stress with force_quiescent_state() being invoked artificially often. Without this fix, unsynchronized access to the ->completed field can cause rcu_process_gp_end() to advance callbacks whose grace period has not yet expired. (Bad idea!) 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 Cc: <stable@kernel.org> # .32.x LKML-Reference: <12571987494069-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/rcutree.h')
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 8a4c1650ad8d..c1891c3cae63 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -84,6 +84,9 @@ struct rcu_node {
long gpnum; /* Current grace period for this node. */
/* This will either be equal to or one */
/* behind the root rcu_node's gpnum. */
+ long completed; /* Last grace period completed for this node. */
+ /* This will either be equal to or one */
+ /* behind the root rcu_node's gpnum. */
unsigned long qsmask; /* CPUs or groups that need to switch in */
/* order for current grace period to proceed.*/
/* In leaf rcu_node, each bit corresponds to */

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