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rtmutex: use a trylock for waiter lock in trylock
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Mike Galbraith captered the following:
| >hardkernel#11 [ffff88017b243e90] _raw_spin_lock at ffffffff815d2596
| >hardkernel#12 [ffff88017b243e90] rt_mutex_trylock at ffffffff815d15be
| >hardkernel#13 [ffff88017b243eb0] get_next_timer_interrupt at ffffffff81063b42
| >hardkernel#14 [ffff88017b243f00] tick_nohz_stop_sched_tick at ffffffff810bd1fd
| >hardkernel#15 [ffff88017b243f70] tick_nohz_irq_exit at ffffffff810bd7d2
| >hardkernel#16 [ffff88017b243f90] irq_exit at ffffffff8105b02d
| >hardkernel#17 [ffff88017b243fb0] reschedule_interrupt at ffffffff815db3dd
| >--- <IRQ stack> ---
| >hardkernel#18 [ffff88017a2a9bc8] reschedule_interrupt at ffffffff815db3dd
| >    [exception RIP: task_blocks_on_rt_mutex+51]
| >hardkernel#19 [ffff88017a2a9ce0] rt_spin_lock_slowlock at ffffffff815d183c
| >hardkernel#20 [ffff88017a2a9da0] lock_timer_base.isra.35 at ffffffff81061cbf
| >hardkernel#21 [ffff88017a2a9dd0] schedule_timeout at ffffffff815cf1ce
| >hardkernel#22 [ffff88017a2a9e50] rcu_gp_kthread at ffffffff810f9bbb
| >hardkernel#23 [ffff88017a2a9ed0] kthread at ffffffff810796d5
| >hardkernel#24 [ffff88017a2a9f50] ret_from_fork at ffffffff815da04c

lock_timer_base() does a try_lock() which deadlocks on the waiter lock
not the lock itself.
This patch takes the waiter_lock with trylock so it should work from interrupt
context as well. If the fastpath doesn't work and the waiter_lock itself is
taken then it seems that the lock itself taken.
This patch also adds a "rt_spin_try_unlock" to keep lockdep happy. If we
managed to take the wait_lock in the first place we should also be able
to take it in the unlock path.

Cc: [email protected]
Reported-by: Mike Galbraith <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
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Sebastian Andrzej Siewior authored and Steven Rostedt committed Dec 18, 2013
1 parent cb40dc0 commit d037a27
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Showing 3 changed files with 29 additions and 5 deletions.
1 change: 1 addition & 0 deletions include/linux/spinlock_rt.h
Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@ extern void __lockfunc rt_spin_lock(spinlock_t *lock);
extern unsigned long __lockfunc rt_spin_lock_trace_flags(spinlock_t *lock);
extern void __lockfunc rt_spin_lock_nested(spinlock_t *lock, int subclass);
extern void __lockfunc rt_spin_unlock(spinlock_t *lock);
extern void __lockfunc rt_spin_unlock_after_trylock_in_irq(spinlock_t *lock);
extern void __lockfunc rt_spin_unlock_wait(spinlock_t *lock);
extern int __lockfunc rt_spin_trylock_irqsave(spinlock_t *lock, unsigned long *flags);
extern int __lockfunc rt_spin_trylock_bh(spinlock_t *lock);
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31 changes: 27 additions & 4 deletions kernel/rtmutex.c
Original file line number Diff line number Diff line change
Expand Up @@ -801,10 +801,8 @@ static void noinline __sched rt_spin_lock_slowlock(struct rt_mutex *lock)
/*
* Slow path to release a rt_mutex spin_lock style
*/
static void noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
static void __sched __rt_spin_lock_slowunlock(struct rt_mutex *lock)
{
raw_spin_lock(&lock->wait_lock);

debug_rt_mutex_unlock(lock);

rt_mutex_deadlock_account_unlock(current);
Expand All @@ -823,6 +821,23 @@ static void noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
rt_mutex_adjust_prio(current);
}

static void noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
{
raw_spin_lock(&lock->wait_lock);
__rt_spin_lock_slowunlock(lock);
}

static void noinline __sched rt_spin_lock_slowunlock_hirq(struct rt_mutex *lock)
{
int ret;

do {
ret = raw_spin_trylock(&lock->wait_lock);
} while (!ret);

__rt_spin_lock_slowunlock(lock);
}

void __lockfunc rt_spin_lock(spinlock_t *lock)
{
rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
Expand Down Expand Up @@ -853,6 +868,13 @@ void __lockfunc rt_spin_unlock(spinlock_t *lock)
}
EXPORT_SYMBOL(rt_spin_unlock);

void __lockfunc rt_spin_unlock_after_trylock_in_irq(spinlock_t *lock)
{
/* NOTE: we always pass in '1' for nested, for simplicity */
spin_release(&lock->dep_map, 1, _RET_IP_);
rt_spin_lock_fastunlock(&lock->lock, rt_spin_lock_slowunlock_hirq);
}

void __lockfunc __rt_spin_unlock(struct rt_mutex *lock)
{
rt_spin_lock_fastunlock(lock, rt_spin_lock_slowunlock);
Expand Down Expand Up @@ -1056,7 +1078,8 @@ rt_mutex_slowtrylock(struct rt_mutex *lock)
{
int ret = 0;

raw_spin_lock(&lock->wait_lock);
if (!raw_spin_trylock(&lock->wait_lock))
return ret;
init_lists(lock);

if (likely(rt_mutex_owner(lock) != current)) {
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2 changes: 1 addition & 1 deletion kernel/timer.c
Original file line number Diff line number Diff line change
Expand Up @@ -1398,7 +1398,7 @@ unsigned long get_next_timer_interrupt(unsigned long now)
expires = base->next_timer;
}
#ifdef CONFIG_PREEMPT_RT_FULL
rt_spin_unlock(&base->lock);
rt_spin_unlock_after_trylock_in_irq(&base->lock);
#else
spin_unlock(&base->lock);
#endif
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