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rcu: handle unstable rdp in rcu_read_unlock_strict()

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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: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
This commit is contained in:
Ankur Arora 2024-12-12 20:06:55 -08:00 committed by Boqun Feng
parent 2c00e1199c
commit fcf0e25ad4
2 changed files with 11 additions and 2 deletions
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2
include/linux/rcupdate.h
View File

@ -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)

11
kernel/rcu/tree_plugin.h
View File

@ -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);