From: Paul E. McKenney Date: Thu, 20 Mar 2008 00:00:57 +0000 (-0700) Subject: rcu: fix misplaced mb() in rcu_enter/exit_nohz() X-Git-Tag: v2.6.25-rc7~79 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ae66be9b71b12f16b84129860d06bbfe37fbec51;p=pandora-kernel.git rcu: fix misplaced mb() in rcu_enter/exit_nohz() In the process of writing up the mechanical proof of correctness for the dynticks/preemptable-RCU interface, I noticed misplaced memory barriers in rcu_enter_nohz() and rcu_exit_nohz(). This patch puts them in the right place and adds a comment. The key thing to keep in mind is that rcu_enter_nohz() is -exiting- the mode that can legally execute RCU read-side critical sections. The memory barrier must be between any potential RCU read-side critical sections and the increment of the per-CPU dynticks_progress_counter, and thus must come -before- this increment. And vice versa for rcu_exit_nohz(). The locking in the scheduler is probably saving us for the moment. Also, switch to smp_mb() - we don't need a barrier for uniprocessor kernels. Signed-off-by: Paul E. McKenney Acked-by: Steven Rostedt Cc: Nick Piggin Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed