Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Julia Cartwright <julia@ni.com>
To:     linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Carsten Emde <C.Emde@osadl.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        John Kacur <jkacur@redhat.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Daniel Wagner <daniel.wagner@siemens.com>,
        tom.zanussi@linux.intel.com, Boqun Feng <boqun.feng@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH RT 05/22] rtmutex: Make rt_mutex_futex_unlock() safe for irq-off callsites
Date:   Mon,  6 Aug 2018 04:17:21 -0500
Message-Id: <bd21741bb5e918e5ed254b9fa869b5523a469b55.1533540554.git.julia@ni.com>
In-Reply-To: <cover.1533540554.git.julia@ni.com>
References: <cover.1533540554.git.julia@ni.com>
MIME-Version: 1.0
Content-Type: text/plain
Received-SPF: None (protection.outlook.com: ni.com does not designate
 permitted sender hosts)
SpamDiagnosticOutput: 1:99
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Aug 2018 09:17:45.1912 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: fffe1a03-37df-497c-c1f2-08d5fb7d7872
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 87ba1f9a-44cd-43a6-b008-6fdb45a5204e
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR04MB0974
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-08-06_05:,,
 signatures=0
X-Proofpoint-Spam-Details: rule=inbound_policy_notspam policy=inbound_policy score=30
 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0
 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0
 mlxlogscore=999 adultscore=0 classifier=spam adjust=30 reason=mlx
 scancount=1 engine=8.0.1-1807170000 definitions=main-1808060100
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

From: Boqun Feng <boqun.feng@gmail.com>

4.9.115-rt94-rc1 stable review patch.
If you have any objection to the inclusion of this patch, let me know.

--- 8< --- 8< --- 8< ---
[ Upstream commit 6b0ef92fee2a3189eba6d6b827b247cb4f6da7e9 ]

When running rcutorture with TREE03 config, CONFIG_PROVE_LOCKING=y, and
kernel cmdline argument "rcutorture.gp_exp=1", lockdep reports a
HARDIRQ-safe->HARDIRQ-unsafe deadlock:

 =============================== WARNING: inconsistent lock state
 4.16.0-rc4+ #1 Not tainted
 --------------------------------
 inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.
 takes:
 __schedule+0xbe/0xaf0
 {IN-HARDIRQ-W} state was registered at:
   _raw_spin_lock+0x2a/0x40
   scheduler_tick+0x47/0xf0
...
 other info that might help us debug this:
  Possible unsafe locking scenario:
        CPU0
        ----
   lock(&rq->lock);
   <Interrupt>
     lock(&rq->lock);
  *** DEADLOCK ***
 1 lock held by rcu_torture_rea/724:
 rcu_torture_read_lock+0x0/0x70
 stack backtrace:
 CPU: 2 PID: 724 Comm: rcu_torture_rea Not tainted 4.16.0-rc4+ #1
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014
 Call Trace:
  lock_acquire+0x90/0x200
  ? __schedule+0xbe/0xaf0
  _raw_spin_lock+0x2a/0x40
  ? __schedule+0xbe/0xaf0
  __schedule+0xbe/0xaf0
  preempt_schedule_irq+0x2f/0x60
  retint_kernel+0x1b/0x2d
 RIP: 0010:rcu_read_unlock_special+0x0/0x680
  ? rcu_torture_read_unlock+0x60/0x60
  __rcu_read_unlock+0x64/0x70
  rcu_torture_read_unlock+0x17/0x60
  rcu_torture_reader+0x275/0x450
  ? rcutorture_booster_init+0x110/0x110
  ? rcu_torture_stall+0x230/0x230
  ? kthread+0x10e/0x130
  kthread+0x10e/0x130
  ? kthread_create_worker_on_cpu+0x70/0x70
  ? call_usermodehelper_exec_async+0x11a/0x150
  ret_from_fork+0x3a/0x50

This happens with the following even sequence:

	preempt_schedule_irq();
	  local_irq_enable();
	  __schedule():
	    local_irq_disable(); // irq off
	    ...
	    rcu_note_context_switch():
	      rcu_note_preempt_context_switch():
	        rcu_read_unlock_special():
	          local_irq_save(flags);
	          ...
		  raw_spin_unlock_irqrestore(...,flags); // irq remains off
	          rt_mutex_futex_unlock():
	            raw_spin_lock_irq();
	            ...
	            raw_spin_unlock_irq(); // accidentally set irq on

	    <return to __schedule()>
	    rq_lock():
	      raw_spin_lock(); // acquiring rq->lock with irq on

which means rq->lock becomes a HARDIRQ-unsafe lock, which can cause
deadlocks in scheduler code.

This problem was introduced by commit 02a7c234e540 ("rcu: Suppress
lockdep false-positive ->boost_mtx complaints"). That brought the user
of rt_mutex_futex_unlock() with irq off.

To fix this, replace the *lock_irq() in rt_mutex_futex_unlock() with
*lock_irq{save,restore}() to make it safe to call rt_mutex_futex_unlock()
with irq off.

Fixes: 02a7c234e540 ("rcu: Suppress lockdep false-positive ->boost_mtx complaints")
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
Link: https://lkml.kernel.org/r/20180309065630.8283-1-boqun.feng@gmail.com
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Julia Cartwright <julia@ni.com>
---
 kernel/locking/rtmutex.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 57361d631749..5e15f5c73637 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -2213,11 +2213,12 @@ void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
 {
 	WAKE_Q(wake_q);
 	WAKE_Q(wake_sleeper_q);
+	unsigned long flags;
 	bool postunlock;
 
-	raw_spin_lock_irq(&lock->wait_lock);
+	raw_spin_lock_irqsave(&lock->wait_lock, flags);
 	postunlock = __rt_mutex_futex_unlock(lock, &wake_q, &wake_sleeper_q);
-	raw_spin_unlock_irq(&lock->wait_lock);
+	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 
 	if (postunlock)
 		rt_mutex_postunlock(&wake_q, &wake_sleeper_q);
-- 
2.18.0