From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
stable <stable@vger.kernel.org>
Subject: Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers
Date: Sun, 24 Sep 2017 12:42:32 -0700 [thread overview]
Message-ID: <CA+55aFyHXW5smbkWdpz-v3n6=9u1+m68YH4rB8Kb99AWaz50Kw@mail.gmail.com> (raw)
In-Reply-To: <20170923205804.098759069@goodmis.org>
On Sat, Sep 23, 2017 at 1:56 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> +
> + /* Page faults can happen in NMI handlers, so check... */
> + if (READ_ONCE(rdtp->dynticks_nmi_nesting))
> + return;
> +
What is the reason for the READ_ONCE() here (and in the other case)?
It doesn't seem to have any actual reason. It's a "stable" per-cpu
value in that even if an NMI were to happen, it gets incremented and
then decremented, so there is nothing really volatile about it
anywhere that I can see.
So the READ_ONCE() seems to be just pure confusion.
What am I missing?
Linus
next prev parent reply other threads:[~2017-09-24 19:42 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-23 20:56 [PATCH 0/4] [GIT PULL] tracing/rcu: Fix save_stack_trace() called when RCU is not watching Steven Rostedt
2017-09-23 20:56 ` [PATCH 1/4] rcu: Allow for page faults in NMI handlers Steven Rostedt
2017-09-24 19:42 ` Linus Torvalds [this message]
2017-09-25 0:03 ` Paul E. McKenney
2017-09-25 0:12 ` Linus Torvalds
2017-09-25 0:26 ` Paul E. McKenney
2017-09-25 0:34 ` Paul E. McKenney
2017-09-25 4:41 ` Steven Rostedt
2017-09-25 4:56 ` Paul E. McKenney
2017-09-26 3:19 ` Paul E. McKenney
2017-09-23 20:56 ` [PATCH 2/4] extable: Consolidate *kernel_text_address() functions Steven Rostedt
2017-09-23 20:56 ` [PATCH 3/4] extable: Enable RCU if it is not watching in kernel_text_address() Steven Rostedt
2017-09-23 20:56 ` [PATCH 4/4] tracing: Remove RCU work arounds from stack tracer Steven Rostedt
-- strict thread matches above, loose matches on Subject: below --
2017-09-22 22:15 [PATCH 0/4] rcu/tracing/extable: Fix stack dump when RCU is not watching Steven Rostedt
2017-09-22 22:15 ` [PATCH 1/4] rcu: Allow for page faults in NMI handlers Steven Rostedt
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