From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
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: Mon, 2 Sep 2019 15:40:03 +0200 [thread overview]
Message-ID: <20190902134003.GA14770@redhat.com> (raw)
In-Reply-To: <87o906wimo.fsf@x220.int.ebiederm.org>
On 08/30, Eric W. Biederman wrote:
>
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -182,6 +182,24 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
> put_task_struct(tsk);
> }
>
> +void put_dead_task_struct(struct task_struct *task)
> +{
> + bool delay = false;
> + unsigned long flags;
> +
> + /* Is the task both reaped and no longer being scheduled? */
> + raw_spin_lock_irqsave(&task->pi_lock, flags);
> + if ((task->state == TASK_DEAD) &&
> + (cmpxchg(&task->exit_state, EXIT_DEAD, EXIT_RCU) == EXIT_DEAD))
> + delay = true;
> + raw_spin_lock_irqrestore(&task->pi_lock, flags);
> +
> + /* If both are true use rcu delay the put_task_struct */
> + if (delay)
> + call_rcu(&task->rcu, delayed_put_task_struct);
> + else
> + put_task_struct(task);
> +}
>
> void release_task(struct task_struct *p)
> {
> @@ -222,76 +240,13 @@ void release_task(struct task_struct *p)
>
> write_unlock_irq(&tasklist_lock);
> release_thread(p);
> - call_rcu(&p->rcu, delayed_put_task_struct);
> + put_dead_task_struct(p);
I had a similar change in mind, see below. This is subjective, but to me
it looks more simple and clean.
Oleg.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8dc1811..1f9b021 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1134,7 +1134,10 @@ struct task_struct {
struct tlbflush_unmap_batch tlb_ubc;
- struct rcu_head rcu;
+ union {
+ bool xxx;
+ struct rcu_head rcu;
+ };
/* Cache last used pipe for splice(): */
struct pipe_inode_info *splice_pipe;
diff --git a/kernel/exit.c b/kernel/exit.c
index a75b6a7..baacfce 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -182,6 +182,11 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
put_task_struct(tsk);
}
+void call_delayed_put_task_struct(struct task_struct *p)
+{
+ if (xchg(&p->xxx, 1))
+ call_rcu(&p->rcu, delayed_put_task_struct);
+}
void release_task(struct task_struct *p)
{
@@ -222,7 +227,7 @@ void release_task(struct task_struct *p)
write_unlock_irq(&tasklist_lock);
release_thread(p);
- call_rcu(&p->rcu, delayed_put_task_struct);
+ call_delayed_put_task_struct(p);
p = leader;
if (unlikely(zap_leader))
diff --git a/kernel/fork.c b/kernel/fork.c
index d8ae0f1..e90f6de 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -900,11 +900,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
if (orig->cpus_ptr == &orig->cpus_mask)
tsk->cpus_ptr = &tsk->cpus_mask;
- /*
- * One for us, one for whoever does the "release_task()" (usually
- * parent)
- */
- refcount_set(&tsk->usage, 2);
+ refcount_set(&tsk->usage, 1);
#ifdef CONFIG_BLK_DEV_IO_TRACE
tsk->btrace_seq = 0;
#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2b037f1..e77389c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3135,7 +3135,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
/* Task is done with its stack. */
put_task_stack(prev);
- put_task_struct(prev);
+ call_delayed_put_task_struct(prev);
}
tick_nohz_task_switch();
next prev parent reply other threads:[~2019-09-02 13:40 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
2019-08-30 16:58 ` Linus Torvalds
2019-08-30 19:36 ` Eric W. Biederman
2019-09-02 13:40 ` Oleg Nesterov [this message]
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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