From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
stable@vger.kernel.org,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Jiri Olsa <jolsa@redhat.com>,
bpf@vger.kernel.org, "Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH 5.9 282/391] rcu-tasks: Enclose task-list scan in rcu_read_lock()
Date: Tue, 3 Nov 2020 21:35:33 +0100 [thread overview]
Message-ID: <20201103203406.066176422@linuxfoundation.org> (raw)
In-Reply-To: <20201103203348.153465465@linuxfoundation.org>
From: Paul E. McKenney <paulmck@kernel.org>
commit f747c7e15d7bc71a967a94ceda686cf2460b69e8 upstream.
The rcu_tasks_trace_postgp() function uses for_each_process_thread()
to scan the task list without the benefit of RCU read-side protection,
which can result in use-after-free errors on task_struct structures.
This error was missed because the TRACE01 rcutorture scenario enables
lockdep, but also builds with CONFIG_PREEMPT_NONE=y. In this situation,
preemption is disabled everywhere, so lockdep thinks everywhere can
be a legitimate RCU reader. This commit therefore adds the needed
rcu_read_lock() and rcu_read_unlock().
Note that this bug can occur only after an RCU Tasks Trace CPU stall
warning, which by default only happens after a grace period has extended
for ten minutes (yes, not a typo, minutes).
Fixes: 4593e772b502 ("rcu-tasks: Add stall warnings for RCU Tasks Trace")
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: <bpf@vger.kernel.org>
Cc: <stable@vger.kernel.org> # 5.7.x
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/rcu/tasks.h | 2 ++
1 file changed, 2 insertions(+)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1078,9 +1078,11 @@ static void rcu_tasks_trace_postgp(struc
if (ret)
break; // Count reached zero.
// Stall warning time, so make a list of the offenders.
+ rcu_read_lock();
for_each_process_thread(g, t)
if (READ_ONCE(t->trc_reader_special.b.need_qs))
trc_add_holdout(t, &holdouts);
+ rcu_read_unlock();
firstreport = true;
list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) {
if (READ_ONCE(t->trc_reader_special.b.need_qs))
prev parent reply other threads:[~2020-11-03 21:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20201103203348.153465465@linuxfoundation.org>
2020-11-03 20:35 ` [PATCH 5.9 280/391] rcu-tasks: Fix grace-period/unlock race in RCU Tasks Trace Greg Kroah-Hartman
2020-11-03 20:35 ` [PATCH 5.9 281/391] rcu-tasks: Fix low-probability task_struct leak Greg Kroah-Hartman
2020-11-03 20:35 ` Greg Kroah-Hartman [this message]
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