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authorThomas Gleixner <tglx@linutronix.de>2016-01-13 11:25:38 +0100
committerThomas Gleixner <tglx@linutronix.de>2016-01-26 11:08:35 +0100
commitb4abf91047cf054f203dcfac97e1038388826937 (patch)
treea018e1a33d72f3c8f154db82acad5b70858417ba /kernel/futex.c
parent92e963f50fc74041b5e9e744c330dca48e04f08d (diff)
downloadlinux-b4abf91047cf054f203dcfac97e1038388826937.tar.bz2
rtmutex: Make wait_lock irq safe
Sasha reported a lockdep splat about a potential deadlock between RCU boosting rtmutex and the posix timer it_lock. CPU0 CPU1 rtmutex_lock(&rcu->rt_mutex) spin_lock(&rcu->rt_mutex.wait_lock) local_irq_disable() spin_lock(&timer->it_lock) spin_lock(&rcu->mutex.wait_lock) --> Interrupt spin_lock(&timer->it_lock) This is caused by the following code sequence on CPU1 rcu_read_lock() x = lookup(); if (x) spin_lock_irqsave(&x->it_lock); rcu_read_unlock(); return x; We could fix that in the posix timer code by keeping rcu read locked across the spinlocked and irq disabled section, but the above sequence is common and there is no reason not to support it. Taking rt_mutex.wait_lock irq safe prevents the deadlock. Reported-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c18
1 files changed, 9 insertions, 9 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 0773f2b23b10..5d6ce6413ef1 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1191,7 +1191,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
if (pi_state->owner != current)
return -EINVAL;
- raw_spin_lock(&pi_state->pi_mutex.wait_lock);
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
/*
@@ -1217,22 +1217,22 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
else if (curval != uval)
ret = -EINVAL;
if (ret) {
- raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
return ret;
}
- raw_spin_lock_irq(&pi_state->owner->pi_lock);
+ raw_spin_lock(&pi_state->owner->pi_lock);
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
- raw_spin_unlock_irq(&pi_state->owner->pi_lock);
+ raw_spin_unlock(&pi_state->owner->pi_lock);
- raw_spin_lock_irq(&new_owner->pi_lock);
+ raw_spin_lock(&new_owner->pi_lock);
WARN_ON(!list_empty(&pi_state->list));
list_add(&pi_state->list, &new_owner->pi_state_list);
pi_state->owner = new_owner;
- raw_spin_unlock_irq(&new_owner->pi_lock);
+ raw_spin_unlock(&new_owner->pi_lock);
- raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
@@ -2127,11 +2127,11 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
* we returned due to timeout or signal without taking the
* rt_mutex. Too late.
*/
- raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
+ raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock);
owner = rt_mutex_owner(&q->pi_state->pi_mutex);
if (!owner)
owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
- raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
+ raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock);
ret = fixup_pi_state_owner(uaddr, q, owner);
goto out;
}