From: Steven Rostedt <rostedt@goodmis.org>
To: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: John Stultz <john.stultz@linaro.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
lkml <linux-kernel@vger.kernel.org>,
Saravana Kannan <saravanak@google.com>,
Todd Kjos <tkjos@google.com>, Stephen Boyd <sboyd@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: On trace_*_rcuidle functions in modules
Date: Wed, 15 Apr 2020 21:24:55 -0400 [thread overview]
Message-ID: <20200415212455.28f22041@oasis.local.home> (raw)
In-Reply-To: <20200416010258.GM20625@builder.lan>
On Wed, 15 Apr 2020 18:02:58 -0700
Bjorn Andersson <bjorn.andersson@linaro.org> wrote:
> Forgive me, but how is this problem related to the fact that the code is
> dynamically loaded, i.e. encapsulated in a module?
It's not.
>
> Per the example earlier in this thread, the thing we're worried about is
> a use after free in the following scenario, right?
>
> cpu_pm_unregister_notifier(my_notifier);
> kfree(my_data);
>
> But a driver implementing this snippet might do this regardless of being
> builtin or module and afaict exiting probe() unsuccessfully or unbinding
> the device would risk triggering this issue?
I know my email was confusing. I was talking about a bug that does not
exist. (There is no bug!)
The reason is that rcu is enabled during the call to the notifiers. The
above assumes that the my_data usage in the notifier callback is
surrounded by rcu_read_lock() (otherwise it's broken regardless of this
code or not). The above unregister will call synchronize_rcu() after it
removes the notifier which will guarantee that the rcu_read_lock()
critical sections would be completed. Then the kfree(my_data) can free
my_data with no possible users.
-- Steve
next prev parent reply other threads:[~2020-04-16 1:25 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-15 2:20 On trace_*_rcuidle functions in modules John Stultz
2020-04-15 2:57 ` Paul E. McKenney
2020-04-15 3:47 ` John Stultz
2020-04-15 13:12 ` Paul E. McKenney
2020-04-15 12:53 ` Steven Rostedt
2020-04-15 19:56 ` John Stultz
2020-04-15 20:14 ` Steven Rostedt
2020-04-15 20:17 ` John Stultz
2020-04-15 20:41 ` Steven Rostedt
2020-04-15 21:02 ` John Stultz
2020-04-15 21:49 ` Steven Rostedt
2020-04-15 22:04 ` Paul E. McKenney
2020-04-15 22:42 ` Peter Zijlstra
2020-04-15 22:53 ` Steven Rostedt
2020-04-15 22:53 ` Paul E. McKenney
2020-04-15 22:51 ` Steven Rostedt
2020-04-15 22:54 ` Paul E. McKenney
2020-04-16 0:06 ` John Stultz
2020-04-16 0:48 ` Steven Rostedt
2020-04-16 1:02 ` Bjorn Andersson
2020-04-16 1:24 ` Steven Rostedt [this message]
2020-04-16 2:17 ` John Stultz
2020-04-15 22:07 ` John Stultz
2020-04-15 22:40 ` Peter Zijlstra
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