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Commit d24209bb authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Improve diagnostics for blocked critical sections in irq 



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 66292405

include/linux/lockdep.h

+6 −1
Original line number Diff line number Diff line
@@ -531,8 +531,13 @@ do { \ 
# define might_lock_read(lock) do { } while (0)

#endif



#ifdef CONFIG_PROVE_RCU

#ifdef CONFIG_LOCKDEP

void lockdep_rcu_suspicious(const char *file, const int line, const char *s);

#else

static inline void

lockdep_rcu_suspicious(const char *file, const int line, const char *s)

{

}

#endif



#endif /* __LINUX_LOCKDEP_H */

include/linux/rcupdate.h

+1 −1
Original line number Diff line number Diff line
@@ -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. */

}



/**

kernel/rcu/tree_plugin.h

+7 −1
Original line number Diff line number Diff line
@@ -334,7 +334,13 @@ void rcu_read_unlock_special(struct task_struct *t) 
	}



	/* Hardware IRQ handlers cannot block, complain if they get here. */

	if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {

	if (in_irq() || in_serving_softirq()) {

		lockdep_rcu_suspicious(__FILE__, __LINE__,

				       "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");

		pr_alert("->rcu_read_unlock_special: %#x (b: %d, nq: %d)\n",

			 t->rcu_read_unlock_special.s,

			 t->rcu_read_unlock_special.b.blocked,

			 t->rcu_read_unlock_special.b.need_qs);

		local_irq_restore(flags);

		return;

	}