6.1-stable review patch. If anyone has any objections, please let me know.
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From: Ankur Arora ankur.a.arora@oracle.com
[ 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 --- include/linux/rcupdate.h | 2 +- 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 aef8c7304d45d..d1c35009831b6 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -97,9 +97,9 @@ 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 4f45562be7b54..3929ef8148c10 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -821,8 +821,17 @@ 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);