1. 26 Jan, 2016 1 commit
    • Thomas Gleixner's avatar
      rtmutex: Make wait_lock irq safe · b4abf910
      Thomas Gleixner authored
      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: default avatarSasha Levin <sasha.levin@oracle.com>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
      b4abf910
  2. 24 Jan, 2016 39 commits