Commit fcf0e25a authored by Ankur Arora's avatar Ankur Arora Committed by Boqun Feng
Browse files

rcu: handle unstable rdp in rcu_read_unlock_strict() 



rcu_read_unlock_strict() can be called with preemption enabled
which can make for an unstable rdp and a racy norm value.

Fix this by dropping the preempt-count in __rcu_read_unlock()
after the call to rcu_read_unlock_strict(), adjusting the
preempt-count check appropriately.

Suggested-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarAnkur Arora <ankur.a.arora@oracle.com>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
parent 2c00e119

include/linux/rcupdate.h

+1 −1
Original line number Diff line number Diff line
@@ -95,9 +95,9 @@ static inline void __rcu_read_lock(void) 


static inline void __rcu_read_unlock(void)

{

	preempt_enable();

	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))

		rcu_read_unlock_strict();

	preempt_enable();

}



static inline int rcu_preempt_depth(void)

kernel/rcu/tree_plugin.h

+10 −1
Original line number Diff line number Diff line
@@ -833,8 +833,17 @@ void rcu_read_unlock_strict(void) 
{

	struct rcu_data *rdp;



	if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)

	if (irqs_disabled() || in_atomic_preempt_off() || !rcu_state.gp_kthread)

		return;



	/*

	 * rcu_report_qs_rdp() can only be invoked with a stable rdp and

	 * from the local CPU.

	 *

	 * The in_atomic_preempt_off() check ensures that we come here holding

	 * the last preempt_count (which will get dropped once we return to

	 * __rcu_read_unlock().

	 */

	rdp = this_cpu_ptr(&rcu_data);

	rdp->cpu_no_qs.b.norm = false;

	rcu_report_qs_rdp(rdp);