Hello, I have some questions about this patch
From: Sebastian Andrzej Siewior <[email protected]>
Date: Tue, 19 Nov 2019 09:25:04 +0100
Subject: [PATCH] locking: Make spinlock_t and rwlock_t a RCU section on RT
On !RT a locked spinlock_t and rwlock_t disables preemption which
implies a RCU read section. There is code that relies on that behaviour.
Add an explicit RCU read section on RT while a sleeping lock (a lock
which would disables preemption on !RT) acquired.
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
---
kernel/locking/rtmutex.c | 6 ++++++
kernel/locking/rwlock-rt.c | 6 ++++++
2 files changed, 12 insertions(+)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1136,6 +1136,7 @@ void __lockfunc rt_spin_lock(spinlock_t
{
spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
+ rcu_read_lock();
migrate_disable();
...............................
Operation of sleep is not allowed in RCU read critical area, If after acquiring a rt-spinlock , try to acquire another one rt-spinlock, This may cause sleep, and trigger RCU warning.
Is there a problem with my analysis or something I missed?
Thanks
Qiang
On 2021-07-26 07:43:33 [+0000], Zhang, Qiang wrote:
> Operation of sleep is not allowed in RCU read critical area, If
> after acquiring a rt-spinlock , try to acquire another one
> rt-spinlock, This may cause sleep, and trigger RCU warning.
>
> Is there a problem with my analysis or something I missed?
This warning is suppressed on RT. Same as on CONFIG_PREEMPT when a task
gets preempted while in a rcu_read_lock() section.
> Thanks
> Qiang
Sebastian