From bcc1f6823be77ce04c0ed12f727a2853c5b37d24 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Wed, 6 Jun 2018 15:31:30 +0200 Subject: [PATCH 347/365] rtmutex: Make rt_mutex_futex_unlock() safe for irq-off callsites [ 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); 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 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 Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Lai Jiangshan Cc: Steven Rostedt Cc: Josh Triplett Cc: Mathieu Desnoyers Cc: "Paul E . McKenney" Link: https://lkml.kernel.org/r/20180309065630.8283-1-boqun.feng@gmail.com Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Julia Cartwright --- 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 7e3b7a99d004..af104105ff07 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); -- 2.28.0