From: Paul E. McKenney Date: Mon, 2 Nov 2009 21:52:28 +0000 (-0800) Subject: rcu: Fix synchronization for rcu_process_gp_end() uses of ->completed counter X-Git-Tag: v2.6.33-rc1~405^2~17 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d09b62dfa336447c52a5ec9bb88adbc479b0f3b8;p=pandora-kernel.git 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 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: # .32.x LKML-Reference: <12571987494069-git-send-email-> Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed