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authorPingfan Liu <kernelfans@gmail.com>2022-09-06 11:36:42 -0700
committerPaul E. McKenney <paulmck@kernel.org>2022-10-18 14:59:57 -0700
commit6343402ac35dd534291a6c82924a4f09cf6cd1e5 (patch)
tree513b8df4827d3f1e8a8f3506bf3559fa00d19952 /kernel/rcu/tree_plugin.h
parentd6fd907a95a73251bd8494e1ba5350342e05e74a (diff)
rcu: Synchronize ->qsmaskinitnext in rcu_boost_kthread_setaffinity()
Once either rcutree_online_cpu() or rcutree_dead_cpu() is invoked concurrently, the following rcu_boost_kthread_setaffinity() race can occur: CPU 1 CPU2 mask = rcu_rnp_online_cpus(rnp); ... mask = rcu_rnp_online_cpus(rnp); ... set_cpus_allowed_ptr(t, cm); set_cpus_allowed_ptr(t, cm); This results in CPU2's update being overwritten by that of CPU1, and thus the possibility of ->boost_kthread_task continuing to run on a to-be-offlined CPU. This commit therefore eliminates this race by relying on the pre-existing acquisition of ->boost_kthread_mutex to serialize the full process of changing the affinity of ->boost_kthread_task. Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Cc: David Woodhouse <dwmw@amazon.co.uk> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: "Jason A. Donenfeld" <Jason@zx2c4.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
-rw-r--r--kernel/rcu/tree_plugin.h5
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index e3142ee35fc6..7b0fe741a088 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1221,11 +1221,13 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
* We don't include outgoingcpu in the affinity set, use -1 if there is
* no outgoing CPU. If there are no CPUs left in the affinity set,
* this function allows the kthread to execute on any CPU.
+ *
+ * Any future concurrent calls are serialized via ->boost_kthread_mutex.
*/
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
struct task_struct *t = rnp->boost_kthread_task;
- unsigned long mask = rcu_rnp_online_cpus(rnp);
+ unsigned long mask;
cpumask_var_t cm;
int cpu;
@@ -1234,6 +1236,7 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
return;
mutex_lock(&rnp->boost_kthread_mutex);
+ mask = rcu_rnp_online_cpus(rnp);
for_each_leaf_node_possible_cpu(rnp, cpu)
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
cpu != outgoingcpu)