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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-04-14 10:40:57 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-05-15 10:29:33 -0700
commit51af970d19f395fc57b82514022126de6c5420cd (patch)
tree20637fb321eddd24f16483bb1ac44b9f8eb5eb57 /kernel/rcu
parentfb31340f8a43a6f2e871164822ef4979b36232ae (diff)
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@linux.vnet.ibm.com> Tested-by: Nicholas Piggin <npiggin@gmail.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.h3
1 files changed, 1 insertions, 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;