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rcu: Improve diagnostics for blocked critical sections in irq

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If an RCU read-side critical section occurs within an interrupt handler
or a softirq handler, it cannot have been preempted.  Therefore, there is
a check in rcu_read_unlock_special() checking for this error.  However,
when this check triggers, it lacks diagnostic information.  This commit
therefore moves rcu_read_unlock()'s lockdep annotation to follow the
call to __rcu_read_unlock() and changes rcu_read_unlock_special()'s
WARN_ON_ONCE() to an lockdep_rcu_suspicious() in order to locate where
the offending RCU read-side critical section began.  In addition, the
value of the ->rcu_read_unlock_special field is printed.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2015-01-21 15:26:03 -08:00
parent 6629240575
commit d24209bb68
3 changed files with 14 additions and 3 deletions
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2
include/linux/rcupdate.h
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@ -942,9 +942,9 @@ static inline void rcu_read_unlock(void)
{
rcu_lockdep_assert(rcu_is_watching(),
"rcu_read_unlock() used illegally while idle");
rcu_lock_release(&rcu_lock_map);
__release(RCU);
__rcu_read_unlock();
rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
}
/**