Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH rcu 2/8] rcu: Synchronize ->qsmaskinitnext in rcu_boost_kthread_setaffinity() | Date | Wed, 19 Oct 2022 15:46:53 -0700 |
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From: Pingfan Liu <kernelfans@gmail.com>
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> --- kernel/rcu/tree_plugin.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index e3142ee35fc6a..7b0fe741a0886 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) -- 2.31.1.189.g2e36527f23
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