Commit ba9f207c authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Paul E. McKenney

rcu: Fix unpaired rcu_irq_enter() from locking selftests

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>
parent 80d02085
...@@ -144,7 +144,7 @@ static void init_shared_classes(void) ...@@ -144,7 +144,7 @@ static void init_shared_classes(void)
#define HARDIRQ_ENTER() \ #define HARDIRQ_ENTER() \
local_irq_disable(); \ local_irq_disable(); \
irq_enter(); \ __irq_enter(); \
WARN_ON(!in_irq()); WARN_ON(!in_irq());
#define HARDIRQ_EXIT() \ #define HARDIRQ_EXIT() \
......
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