diff options
| author | Ankur Arora <ankur.a.arora@oracle.com> | 2024-12-12 20:06:55 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-05-29 11:03:02 +0200 |
| commit | fcabb696743a4ec2e95531a90a2c0aeec2140a36 (patch) | |
| tree | 9f03c059eb79e8be6fa4d5b9e545deff902fb796 | |
| parent | 5cdaa970d73a4428531ebdd31934f4f081dd3916 (diff) | |
rcu: handle unstable rdp in rcu_read_unlock_strict()
[ Upstream commit fcf0e25ad4c8d14d2faab4d9a17040f31efce205 ]
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | include/linux/rcupdate.h | 2 | ||||
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 11 |
2 files changed, 11 insertions, 2 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index bd69ddc102fb..0844ab328851 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -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) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 75ba4d5788c0..304e3405e6ec 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -832,8 +832,17 @@ 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); |