From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Peter Zijlstra <peterz@infradead.org>,
Chris Metcalf <cmetcalf@ezchip.com>,
Christoph Lameter <cl@linux.com>, Kirill Tkhai <tkhai@yandex.ru>,
Mike Galbraith <efault@gmx.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] Use of probe_kernel_address() in task_rcu_dereference() without checking return value
Date: Fri, 30 Aug 2019 18:44:37 +0200 [thread overview]
Message-ID: <20190830164436.GD2634@redhat.com> (raw)
In-Reply-To: <CAHk-=wiZY53ac=mp8R0gjqyUd4ksD3tGHsUS9gvoHiJOT5_cEg@mail.gmail.com>
On 08/30, Linus Torvalds wrote:
>
> But yes, your hack is I guess optimal for this particular case where
> you simply can depend on "we know the pointer was valid, we just don't
> know if it was freed".
>
> Hmm. Don't we RCU-free the task struct? Because then we don't even
> need to care about CONFIG_DEBUG_PAGEALLOC. We can just always access
> the pointer as long as we have the RCU read lock.
For example,
rcu_read_lock();
p = task_rcu_dereference(&cpu_rq(cpu)->curr);
rcu_read_unlock();
->curr is not protected by RCU, the last schedule does put_task_struct()
in finish_task_switch().
Of course we can change this and add another call_rcu (actually we can do
better), and after that we do not need task_rcu_dereference() at all.
Oleg.
next prev parent reply other threads:[~2019-08-30 16:44 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-30 14:08 [BUG] Use of probe_kernel_address() in task_rcu_dereference() without checking return value Russell King - ARM Linux admin
2019-08-30 15:24 ` Oleg Nesterov
2019-08-30 15:30 ` Linus Torvalds
2019-08-30 15:40 ` Russell King - ARM Linux admin
2019-08-30 15:43 ` Linus Torvalds
2019-08-30 15:41 ` Linus Torvalds
2019-08-30 16:09 ` Oleg Nesterov
2019-08-30 16:21 ` Linus Torvalds
2019-08-30 16:44 ` Oleg Nesterov [this message]
2019-08-30 16:58 ` Linus Torvalds
2019-08-30 19:36 ` Eric W. Biederman
2019-09-02 13:40 ` Oleg Nesterov
2019-09-02 13:53 ` Peter Zijlstra
2019-09-02 14:44 ` Oleg Nesterov
2019-09-02 16:20 ` Peter Zijlstra
2019-09-02 17:04 ` Eric W. Biederman
2019-09-02 17:34 ` Linus Torvalds
2019-09-03 4:50 ` [PATCH 0/3] task: Making tasks on the runqueue rcu protected Eric W. Biederman
2019-09-03 4:51 ` [PATCH 1/3] task: Add a count of task rcu users Eric W. Biederman
2019-09-04 14:36 ` Oleg Nesterov
2019-09-04 14:44 ` Frederic Weisbecker
2019-09-04 15:32 ` Oleg Nesterov
2019-09-04 16:33 ` Frederic Weisbecker
2019-09-04 18:20 ` Linus Torvalds
2019-09-05 14:59 ` Frederic Weisbecker
2019-09-03 4:52 ` [PATCH 2/3] task: RCU protect tasks on the runqueue Eric W. Biederman
2019-09-03 7:41 ` Peter Zijlstra
2019-09-03 7:47 ` Peter Zijlstra
2019-09-03 16:44 ` Eric W. Biederman
2019-09-03 17:08 ` Linus Torvalds
2019-09-03 18:13 ` Eric W. Biederman
2019-09-03 19:18 ` Linus Torvalds
2019-09-03 20:06 ` Peter Zijlstra
2019-09-03 21:32 ` Paul E. McKenney
2019-09-05 20:02 ` Eric W. Biederman
2019-09-05 20:55 ` Paul E. McKenney
2019-09-06 7:07 ` Peter Zijlstra
2019-09-09 12:22 ` Eric W. Biederman
2019-09-25 7:36 ` Peter Zijlstra
2019-09-27 8:10 ` [tip: sched/urgent] tasks, sched/core: RCUify the assignment of rq->curr tip-bot2 for Eric W. Biederman
2019-09-03 19:42 ` [PATCH 2/3] task: RCU protect tasks on the runqueue Peter Zijlstra
2019-09-14 12:31 ` [PATCH v2 1/4] task: Add a count of task rcu users Eric W. Biederman
2019-09-14 12:31 ` [PATCH v2 2/4] task: Ensure tasks are available for a grace period after leaving the runqueue Eric W. Biederman
2019-09-14 12:32 ` [PATCH v2 3/4] task: With a grace period after finish_task_switch, remove unnecessary code Eric W. Biederman
2019-09-04 14:22 ` [PATCH 2/3] task: RCU protect tasks on the runqueue Frederic Weisbecker
2019-09-03 4:52 ` [PATCH 3/3] task: Clean house now that tasks on the runqueue are rcu protected Eric W. Biederman
2019-09-03 9:45 ` kbuild test robot
2019-09-03 13:06 ` Oleg Nesterov
2019-09-03 13:58 ` [PATCH 0/3] task: Making tasks on the runqueue " Oleg Nesterov
2019-09-03 15:44 ` Linus Torvalds
2019-09-03 19:46 ` Peter Zijlstra
[not found] ` <87muf7f4bf.fsf_-_@x220.int.ebiederm.org>
2019-09-14 12:33 ` [PATCH v2 1/4] task: Add a count of task rcu users Eric W. Biederman
2019-09-15 13:54 ` Paul E. McKenney
2019-09-27 8:10 ` [tip: sched/urgent] tasks: Add a count of task RCU users tip-bot2 for Eric W. Biederman
2019-09-14 12:33 ` [PATCH v2 2/4] task: Ensure tasks are available for a grace period after leaving the runqueue Eric W. Biederman
2019-09-15 14:07 ` Paul E. McKenney
2019-09-15 14:09 ` Paul E. McKenney
2019-09-27 8:10 ` [tip: sched/urgent] tasks, sched/core: " tip-bot2 for Eric W. Biederman
2019-09-14 12:34 ` [PATCH v2 3/4] task: With a grace period after finish_task_switch, remove unnecessary code Eric W. Biederman
2019-09-15 14:32 ` Paul E. McKenney
2019-09-15 17:07 ` Linus Torvalds
2019-09-15 18:47 ` Paul E. McKenney
2019-09-27 8:10 ` [tip: sched/urgent] tasks, sched/core: With a grace period after finish_task_switch(), " tip-bot2 for Eric W. Biederman
2019-09-14 12:35 ` [PATCH v2 4/4] task: RCUify the assignment of rq->curr Eric W. Biederman
2019-09-15 14:41 ` Paul E. McKenney
2019-09-15 17:59 ` Eric W. Biederman
2019-09-15 18:25 ` Eric W. Biederman
2019-09-15 18:48 ` Paul E. McKenney
2019-09-20 23:02 ` Frederic Weisbecker
2019-09-26 1:49 ` Eric W. Biederman
2019-09-26 12:42 ` Frederic Weisbecker
2019-09-14 17:43 ` [PATCH v2 0/4] task: Making tasks on the runqueue rcu protected Linus Torvalds
2019-09-17 17:38 ` Eric W. Biederman
2019-09-25 7:51 ` Peter Zijlstra
2019-09-26 1:11 ` Eric W. Biederman
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