diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2008-03-19 17:00:57 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-03-19 18:53:36 -0700 |
| commit | ae66be9b71b12f16b84129860d06bbfe37fbec51 (patch) | |
| tree | 5bf1d1722f0d83bb4c30621b031437a141a15af1 /include | |
| parent | b691da35ba94d5fa0a32589d99b6546be2bf4cfa (diff) | |
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 <paulmck@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/rcupreempt.h | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h index 01152ed532c..d038aa6e5ee 100644 --- a/include/linux/rcupreempt.h +++ b/include/linux/rcupreempt.h @@ -87,15 +87,15 @@ DECLARE_PER_CPU(long, dynticks_progress_counter); static inline void rcu_enter_nohz(void) { + smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */ __get_cpu_var(dynticks_progress_counter)++; WARN_ON(__get_cpu_var(dynticks_progress_counter) & 0x1); - mb(); } static inline void rcu_exit_nohz(void) { - mb(); __get_cpu_var(dynticks_progress_counter)++; + smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */ WARN_ON(!(__get_cpu_var(dynticks_progress_counter) & 0x1)); } |