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* Question on (locking: Make spinlock_t and rwlock_t a RCU section on RT)
@ 2021-07-26  7:43 Zhang, Qiang
  2021-07-30 14:44 ` Sebastian Andrzej Siewior
  0 siblings, 1 reply; 2+ messages in thread
From: Zhang, Qiang @ 2021-07-26  7:43 UTC (permalink / raw)
  To: Sebastian Andrzej Siewior; +Cc: linux-rt-users, LKML, Thomas Gleixner

Hello,  I have some questions about this patch 

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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 <bigeasy@linutronix.de>
---
 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

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2021-07-26  7:43 Question on (locking: Make spinlock_t and rwlock_t a RCU section on RT) Zhang, Qiang
2021-07-30 14:44 ` Sebastian Andrzej Siewior

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