• Frederic Weisbecker's avatar
    rcu: Fix unpaired rcu_irq_enter() from locking selftests · ba9f207c
    Frederic Weisbecker authored
    HARDIRQ_ENTER() maps to irq_enter() which calls rcu_irq_enter().
    But HARDIRQ_EXIT() maps to __irq_exit() which doesn't call
    rcu_irq_exit().
    
    So for every locking selftest that simulates hardirq disabled,
    we create an imbalance in the rcu extended quiescent state
    internal state.
    
    As a result, after the first missing rcu_irq_exit(), subsequent
    irqs won't exit dyntick-idle mode after leaving the interrupt
    handler.  This means that RCU won't see the affected CPU as being
    in an extended quiescent state, resulting in long grace-period
    delays (as in grace periods extending for hours).
    
    To fix this, just use __irq_enter() to simulate the hardirq
    context. This is sufficient for the locking selftests as we
    don't need to exit any extended quiescent state or perform
    any check that irqs normally do when they wake up from idle.
    
    As a side effect, this patch makes it possible to restore
    "rcu: Decrease memory-barrier usage based on semi-formal proof",
    which eventually helped finding this bug.
    Reported-and-tested-by: default avatarYinghai Lu <yinghai@kernel.org>
    Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Stable <stable@kernel.org>
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    ba9f207c
locking-selftest.c 28.6 KB