From: Oleg Nesterov <oleg@redhat.com>
To: Kirill Tkhai <ktkhai@parallels.com>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Vladimir Davydov <vdavydov@parallels.com>,
Kirill Tkhai <tkhai@yandex.ru>
Subject: introduce task_rcu_dereference?
Date: Wed, 22 Oct 2014 23:30:41 +0200 [thread overview]
Message-ID: <20141022213041.GA25467@redhat.com> (raw)
In-Reply-To: <1413962231.19914.130.camel@tkhai>
On 10/22, Kirill Tkhai wrote:
>
> Unlocked access to dst_rq->curr in task_numa_compare() is racy.
> If curr task is exiting this may be a reason of use-after-free:
Thanks.
And as you pointed out, there are other examples of unlocked
foreign_rq->curr usage.
So, Kirill, Peter, do you think that the patch below can help? Can
we change task_numa_group() and ->select_task_rq() to do nothing if
rq_curr_rcu_safe() returns NULL? It seems we can...
task_numa_compare() can use it too, we can make another patch on
top of this one.
- Obviously just for the early review. Lacks the changelog
and the comments (at least).
- Once again, I won't insist on probe_slab_address(). We can
add SDBR and change task_rcu_dereference() to simply read
->sighand.
- Also, I won't argue if you think that we do not need a
generic helper. In this case we can move this logic into
rq_curr_rcu_safe() and it will be a bit simpler.
- OTOH, I am not sure we need rq_curr_rcu_safe(). The callers
can just use task_rcu_dereference() and check IS_ERR_OR_NULL,
I guess retry doesn't buy too much in this case.
Or do you think we need something else?
Oleg.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 857ba40..0ba420e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2300,6 +2300,7 @@ extern void block_all_signals(int (*notifier)(void *priv), void *priv,
sigset_t *mask);
extern void unblock_all_signals(void);
extern void release_task(struct task_struct * p);
+extern struct task_struct *task_rcu_dereference(struct task_struct **ptask);
extern int send_sig_info(int, struct siginfo *, struct task_struct *);
extern int force_sigsegv(int, struct task_struct *);
extern int force_sig_info(int, struct siginfo *, struct task_struct *);
diff --git a/kernel/exit.c b/kernel/exit.c
index 32c58f7..4aa00c7 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -213,6 +213,37 @@ repeat:
goto repeat;
}
+struct task_struct *task_rcu_dereference(struct task_struct **ptask)
+{
+ struct task_struct *task;
+ struct sighand_struct *sighand;
+
+ task = rcu_dereference(*ptask);
+ if (!task)
+ return NULL;
+
+ /* If it fails the check below must fail too */
+ probe_slab_address(&task->sighand, sighand);
+ /*
+ * Pairs with atomic_dec_and_test() in put_task_struct(task).
+ * If we have read the freed/reused memory, we must see that
+ * the pointer was updated. The caller might want to retry in
+ * this case.
+ */
+ smp_rmb();
+ if (unlikely(task != ACCESS_ONCE(*ptask)))
+ return ERR_PTR(-EAGAIN);
+
+ /*
+ * release_task(task) was already called; potentially before
+ * the caller took rcu_read_lock() and in this case it can be
+ * freed before rcu_read_unlock().
+ */
+ if (!sighand)
+ return ERR_PTR(-EINVAL);
+ return task;
+}
+
/*
* This checks not only the pgrp, but falls back on the pid if no
* satisfactory pgrp is found. I dunno - gdb doesn't work correctly
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 579712f..249c0c1 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -655,6 +655,18 @@ DECLARE_PER_CPU(struct rq, runqueues);
#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
#define raw_rq() (&__raw_get_cpu_var(runqueues))
+static inline struct task_struct *rq_curr_rcu_safe(struct rq *rq)
+{
+ for (;;) {
+ struct task_struct *curr = task_rcu_dereference(&rq->curr);
+ /* NULL is not possible */
+ if (likely(!IS_ERR(curr)))
+ return curr;
+ if (PTR_ERR(curr) != -EAGAIN)
+ return NULL;
+ }
+}
+
static inline u64 rq_clock(struct rq *rq)
{
return rq->clock;
next prev parent reply other threads:[~2014-10-22 21:34 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-22 7:17 [PATCH v4] sched/numa: fix unsafe get_task_struct() in task_numa_assign() Kirill Tkhai
2014-10-22 21:30 ` Oleg Nesterov [this message]
2014-10-22 22:23 ` introduce task_rcu_dereference? Oleg Nesterov
2014-10-23 18:15 ` Oleg Nesterov
2014-10-23 8:10 ` Kirill Tkhai
2014-10-23 18:18 ` Oleg Nesterov
2014-10-24 7:51 ` Kirill Tkhai
2014-10-27 19:53 ` [PATCH 0/3] introduce task_rcu_dereference() Oleg Nesterov
2014-10-27 19:54 ` [PATCH 1/3] probe_kernel_address() can use __probe_kernel_read() Oleg Nesterov
2014-10-27 19:54 ` [PATCH 2/3] introduce probe_slab_address() Oleg Nesterov
2014-10-27 19:21 ` Christoph Lameter
2014-10-28 5:44 ` Kirill Tkhai
2014-10-28 5:48 ` Kirill Tkhai
2014-10-28 15:01 ` Peter Zijlstra
2014-10-28 17:56 ` Kirill Tkhai
2014-10-28 18:00 ` Kirill Tkhai
2014-10-28 19:55 ` Oleg Nesterov
2014-10-28 20:12 ` Oleg Nesterov
2014-10-29 5:10 ` Kirill Tkhai
2014-10-27 19:54 ` [PATCH 3/3] introduce task_rcu_dereference() Oleg Nesterov
2014-10-28 6:22 ` Kirill Tkhai
2016-05-18 17:02 ` Peter Zijlstra
2016-05-18 18:23 ` Oleg Nesterov
2016-05-18 19:10 ` Peter Zijlstra
2016-05-18 19:57 ` Oleg Nesterov
2016-05-26 11:34 ` Peter Zijlstra
2016-06-03 10:49 ` [tip:sched/core] sched/fair: Use task_rcu_dereference() tip-bot for Oleg Nesterov
2016-06-03 10:48 ` [tip:sched/core] sched/api: Introduce task_rcu_dereference() and try_get_task_struct() tip-bot for Oleg Nesterov
2014-10-28 11:02 ` [tip:sched/core] sched/numa: Fix unsafe get_task_struct() in task_numa_assign() tip-bot for Kirill Tkhai
2014-11-08 3:48 ` [PATCH v4] sched/numa: fix " Sasha Levin
2014-11-09 14:07 ` Kirill Tkhai
2014-11-10 10:03 ` Peter Zijlstra
2014-11-10 15:48 ` Sasha Levin
2014-11-10 16:01 ` Peter Zijlstra
2014-11-16 9:50 ` [tip:sched/urgent] sched/numa: Avoid selecting oneself as swap target tip-bot for Peter Zijlstra
2014-11-10 16:03 ` [PATCH v4] sched/numa: fix unsafe get_task_struct() in task_numa_assign() Peter Zijlstra
2014-11-10 16:09 ` Sasha Levin
2014-11-10 16:16 ` Peter Zijlstra
2014-11-10 16:10 ` Kirill Tkhai
2014-11-10 16:36 ` Kirill Tkhai
2014-11-10 16:44 ` Sasha Levin
2014-11-10 20:01 ` Kirill Tkhai
2014-11-12 9:49 ` Kirill Tkhai
2014-11-15 2:38 ` Sasha Levin
2014-11-18 17:30 ` Sasha Levin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20141022213041.GA25467@redhat.com \
--to=oleg@redhat.com \
--cc=ktkhai@parallels.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=tkhai@yandex.ru \
--cc=vdavydov@parallels.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).