Commit-ID: 51af970d19f395fc57b82514022126de6c5420cd
Gitweb: https://git.kernel.org/tip/51af970d19f395fc57b82514022126de6c5420cd
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Sat, 14 Apr 2018 10:40:57 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue, 15 May 2018 10:29:33 -0700
rcu: Avoid losing ->need_future_gp[] values due to GP start/end races
The rcu_cbs_completed() function provides the value of ->completed
at which new callbacks can safely be invoked. This is recorded in
two-element ->need_future_gp[] arrays in the rcu_node structure, and
the elements of these arrays corresponding to the just-completed grace
period are zeroed at the end of that grace period. However, the
rcu_cbs_completed() function can return the current ->completed value
plus either one or two, so it is possible for the corresponding
->need_future_gp[] entry to be cleared just after it was set, thus
losing a request for a future grace period.
This commit avoids this race by expanding ->need_future_gp[] to four
elements.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Tested-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
kernel/rcu/tree.h | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index bd1103763551..952cd0c223fe 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -150,8 +150,7 @@ struct rcu_node {
struct swait_queue_head nocb_gp_wq[2];
/* Place for rcu_nocb_kthread() to wait GP. */
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
- int need_future_gp[2];
- /* Counts of upcoming no-CB GP requests. */
+ int need_future_gp[4]; /* Counts of upcoming no-CB GP requests. */
raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
spinlock_t exp_lock ____cacheline_internodealigned_in_smp;
--
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