From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Nicholas Mc Guire <der.herr@hofr.at>,
Kevin Hao <haokexin@gmail.com>,
linux-rt-users@vger.kernel.org, rostedt@goodmis.org
Subject: Re: [PATCH v3.14-rt] netpoll: guard the access to dev->npinfo with rcu_read_lock/unlock_bh() for CONFIG_PREEMPT_RT_FULL=y
Date: Tue, 17 Feb 2015 15:29:53 +0100 [thread overview]
Message-ID: <20150217142953.GS26177@linutronix.de> (raw)
In-Reply-To: <20141203211911.GR25340@linux.vnet.ibm.com>
* Paul E. McKenney | 2014-12-03 13:19:11 [-0800]:
>> Is that not actually a bug indepedent of RT ?
>> without the rcu_read_lock/unlock who says that the
>> rcu_dereference is still valid at this point ?
>> I though that if bh are already disabled you still
>> need the read_lock. disabled bh would allow to "downgrad"
>> the rcu_read_lock_bh to rcu_read_lock but you still need it.
>
>In vanilla kernels, anything that disables BH acts as rcu_read_lock_bh().
>So yes, you can have cases where rcu_read_lock_bh() is needed only in
>the -rt kernel.
But it won't hurt mainline using rcu_read_lock_bh() around
rcu_dereference_bh() right?
I am not going to apply this because that code is gone shortly after
v3.14 was released. The fm10k however does the same thing so atleast RCU
knows when to scream :)
>
> Thanx, Paul
Sebastian
next prev parent reply other threads:[~2015-02-17 14:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-03 12:05 [PATCH v3.14-rt] netpoll: guard the access to dev->npinfo with rcu_read_lock/unlock_bh() for CONFIG_PREEMPT_RT_FULL=y Kevin Hao
2014-12-03 12:50 ` Nicholas Mc Guire
2014-12-03 21:19 ` Paul E. McKenney
2015-02-17 14:29 ` Sebastian Andrzej Siewior [this message]
2015-02-17 16:16 ` Paul E. McKenney
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