The patch titled
rcu: fix misplaced mb() in rcu_enter/exit_nohz()
has been removed from the -mm tree. Its filename was
rcu-fix-misplaced-mb-in-rcu_enter-exit_nohz.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: rcu: fix misplaced mb() in rcu_enter/exit_nohz()
From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Acked-by: Steven Rostedt <srostedt@xxxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/rcupreempt.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff -puN include/linux/rcupreempt.h~rcu-fix-misplaced-mb-in-rcu_enter-exit_nohz include/linux/rcupreempt.h
--- a/include/linux/rcupreempt.h~rcu-fix-misplaced-mb-in-rcu_enter-exit_nohz
+++ a/include/linux/rcupreempt.h
@@ -87,15 +87,15 @@ DECLARE_PER_CPU(long, dynticks_progress_
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));
}
_
Patches currently in -mm which might be from paulmck@xxxxxxxxxxxxxxxxxx are
origin.patch
kthread-call-wake_up_process-without-the-lock-being-held.patch
add-rcu_assign_index-if-ever-needed.patch
add-rcu_assign_index-if-ever-needed-fix.patch
rcu-split-listh-and-move-rcu-protected-lists-into-rculisth.patch
isolate-ratelimit-from-printkc-for-other-use.patch
add-warn_on_secs-macro.patch
add-warn_on_secs-macro-simplification.patch
add-warn_on_secs-macro-simplification-fix.patch
use-warn_on_secs-in-rcupreempth.patch
lock_task_sighand-add-rcu-lock-unlock.patch
k_getrusage-dont-take-rcu_read_lock.patch
do_task_stat-dont-take-rcu_read_lock.patch
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