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Merge branch 'rcu/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/urgent 

Pull an RCU fix from Paul E. McKenney:

 "This series contains a single commit fixing an initialization bug
  reported by Amit Shah and fixed by Pranith Kumar (and tested by Amit).
  This bug results in a boot-time hang in callback-offloaded configurations
  where callbacks were posted before the offloading ('rcuo') kthreads
  were created."

Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ingo Molnar 2014-09-03 10:46:51 +02:00
parent 69e273c0b0 11ed7f934c
commit 651bc1a474
2 changed files with 12 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
kernel/rcu/tree.h
View File

@ -358,7 +358,7 @@ struct rcu_data {
struct rcu_head **nocb_gp_tail;
long nocb_gp_count;
long nocb_gp_count_lazy;
bool nocb_leader_wake; /* Is the nocb leader thread awake? */
bool nocb_leader_sleep; /* Is the nocb leader thread asleep? */
struct rcu_data *nocb_next_follower;
/* Next follower in wakeup chain. */

22
kernel/rcu/tree_plugin.h
View File

@ -2074,9 +2074,9 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
if (!ACCESS_ONCE(rdp_leader->nocb_kthread))
return;
if (!ACCESS_ONCE(rdp_leader->nocb_leader_wake) || force) {
if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {
/* Prior xchg orders against prior callback enqueue. */
ACCESS_ONCE(rdp_leader->nocb_leader_wake) = true;
ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;
wake_up(&rdp_leader->nocb_wq);
}
}
@ -2253,7 +2253,7 @@ wait_again:
if (!rcu_nocb_poll) {
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
wait_event_interruptible(my_rdp->nocb_wq,
ACCESS_ONCE(my_rdp->nocb_leader_wake));
!ACCESS_ONCE(my_rdp->nocb_leader_sleep));
/* Memory barrier handled by smp_mb() calls below and repoll. */
} else if (firsttime) {
firsttime = false; /* Don't drown trace log with "Poll"! */
@ -2292,12 +2292,12 @@ wait_again:
schedule_timeout_interruptible(1);
/* Rescan in case we were a victim of memory ordering. */
my_rdp->nocb_leader_wake = false;
smp_mb(); /* Ensure _wake false before scan. */
my_rdp->nocb_leader_sleep = true;
smp_mb(); /* Ensure _sleep true before scan. */
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
if (ACCESS_ONCE(rdp->nocb_head)) {
/* Found CB, so short-circuit next wait. */
my_rdp->nocb_leader_wake = true;
my_rdp->nocb_leader_sleep = false;
break;
}
goto wait_again;
@ -2307,17 +2307,17 @@ wait_again:
rcu_nocb_wait_gp(my_rdp);
/*
* We left ->nocb_leader_wake set to reduce cache thrashing.
* We clear it now, but recheck for new callbacks while
* We left ->nocb_leader_sleep unset to reduce cache thrashing.
* We set it now, but recheck for new callbacks while
* traversing our follower list.
*/
my_rdp->nocb_leader_wake = false;
smp_mb(); /* Ensure _wake false before scan of ->nocb_head. */
my_rdp->nocb_leader_sleep = true;
smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
/* Each pass through the following loop wakes a follower, if needed. */
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
if (ACCESS_ONCE(rdp->nocb_head))
my_rdp->nocb_leader_wake = true; /* No need to wait. */
my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
if (!rdp->nocb_gp_head)
continue; /* No CBs, so no need to wake follower. */