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linux/kernel/locking
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Boqun Feng 6b0ef92fee rtmutex: Make rt_mutex_futex_unlock() safe for irq-off callsites 
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 02a7c234e5 ("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: 02a7c234e5 ("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
2018-03-09 11:06:16 +01:00
..
lockdep_internals.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
lockdep_proc.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
lockdep_states.h locking/lockdep: Rework FS_RECLAIM annotation 2017-08-10 12:29:03 +02:00
lockdep.c Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-01-30 10:44:56 -08:00
locktorture.c torture: Eliminate torture_runnable and perf_runnable 2017-12-11 09:18:29 -08:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mcs_spinlock.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mutex-debug.c locking/mutex: Rework mutex::owner 2016-10-25 11:31:50 +02:00
mutex-debug.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mutex.c mutex, futex: adjust kernel-doc markups to generate ReST 2017-05-16 08:43:25 -03:00
mutex.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
osq_lock.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
percpu-rwsem.c locking/percpu-rwsem: Replace waitqueue with rcuwait 2017-01-14 11:14:35 +01:00
qrwlock.c locking/qrwlock: Prevent slowpath writers getting held up by fastpath 2017-10-25 10:57:25 +02:00
qspinlock_paravirt.h locking/pvqspinlock: Implement hybrid PV queued/unfair locks 2017-11-08 10:10:04 +01:00
qspinlock_stat.h sched/headers: Prepare for new header dependencies before moving code to <linux/sched/clock.h> 2017-03-02 08:42:27 +01:00
qspinlock.c locking/qspinlock: Ensure node->count is updated before initialising node 2018-02-13 14:50:14 +01:00
rtmutex_common.h futex: Avoid violating the 10th rule of futex 2018-01-14 18:49:16 +01:00
rtmutex-debug.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rtmutex-debug.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rtmutex.c rtmutex: Make rt_mutex_futex_unlock() safe for irq-off callsites 2018-03-09 11:06:16 +01:00
rtmutex.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rwsem-spinlock.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rwsem-xadd.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rwsem.c Merge branch 'linus' into locking/core, to resolve conflicts 2017-11-07 10:32:44 +01:00
rwsem.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
semaphore.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02 08:42:34 +01:00
spinlock_debug.c locking/spinlock/debug: Remove spinlock lockup detection code 2017-02-10 09:09:49 +01:00
spinlock.c locking/core: Remove break_lock field when CONFIG_GENERIC_LOCKBREAK=y 2017-12-12 11:24:01 +01:00
test-ww_mutex.c mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00