Commit f6f48e18 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions 



nmi_enter() does lockdep_off() and hence lockdep ignores everything.

And NMI context makes it impossible to do full IN-NMI tracking like we
do IN-HARDIRQ, that could result in graph_lock recursion.

However, since look_up_lock_class() is lockless, we can find the class
of a lock that has prior use and detect IN-NMI after USED, just not
USED after IN-NMI.

NOTE: By shifting the lockdep_off() recursion count to bit-16, we can
easily differentiate between actual recursion and off.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Link: https://lkml.kernel.org/r/20200221134215.090538203@infradead.org
parent 248efb21

kernel/locking/lockdep.c

+59 −3
Original line number Diff line number Diff line
@@ -393,15 +393,22 @@ void lockdep_init_task(struct task_struct *task) 
	task->lockdep_recursion = 0;

}



/*

 * Split the recrursion counter in two to readily detect 'off' vs recursion.

 */

#define LOCKDEP_RECURSION_BITS	16

#define LOCKDEP_OFF		(1U << LOCKDEP_RECURSION_BITS)

#define LOCKDEP_RECURSION_MASK	(LOCKDEP_OFF - 1)



void lockdep_off(void)

{

	current->lockdep_recursion++;

	current->lockdep_recursion += LOCKDEP_OFF;

}

EXPORT_SYMBOL(lockdep_off);



void lockdep_on(void)

{

	current->lockdep_recursion--;

	current->lockdep_recursion -= LOCKDEP_OFF;

}

EXPORT_SYMBOL(lockdep_on);
@@ -597,6 +604,7 @@ static const char *usage_str[] = 
#include "lockdep_states.h"

#undef LOCKDEP_STATE

	[LOCK_USED] = "INITIAL USE",

	[LOCK_USAGE_STATES] = "IN-NMI",

};

#endif
@@ -809,6 +817,7 @@ static int count_matching_names(struct lock_class *new_class) 
	return count + 1;

}



/* used from NMI context -- must be lockless */

static inline struct lock_class *

look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)

{
@@ -4720,6 +4729,36 @@ void lock_downgrade(struct lockdep_map *lock, unsigned long ip) 
}

EXPORT_SYMBOL_GPL(lock_downgrade);



/* NMI context !!! */

static void verify_lock_unused(struct lockdep_map *lock, struct held_lock *hlock, int subclass)

{

#ifdef CONFIG_PROVE_LOCKING

	struct lock_class *class = look_up_lock_class(lock, subclass);



	/* if it doesn't have a class (yet), it certainly hasn't been used yet */

	if (!class)

		return;



	if (!(class->usage_mask & LOCK_USED))

		return;



	hlock->class_idx = class - lock_classes;



	print_usage_bug(current, hlock, LOCK_USED, LOCK_USAGE_STATES);

#endif

}



static bool lockdep_nmi(void)

{

	if (current->lockdep_recursion & LOCKDEP_RECURSION_MASK)

		return false;



	if (!in_nmi())

		return false;



	return true;

}



/*

 * We are not always called with irqs disabled - do that here,

 * and also avoid lockdep recursion:
@@ -4730,8 +4769,25 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass, 
{

	unsigned long flags;



	if (unlikely(current->lockdep_recursion))

	if (unlikely(current->lockdep_recursion)) {

		/* XXX allow trylock from NMI ?!? */

		if (lockdep_nmi() && !trylock) {

			struct held_lock hlock;



			hlock.acquire_ip = ip;

			hlock.instance = lock;

			hlock.nest_lock = nest_lock;

			hlock.irq_context = 2; // XXX

			hlock.trylock = trylock;

			hlock.read = read;

			hlock.check = check;

			hlock.hardirqs_off = true;

			hlock.references = 0;



			verify_lock_unused(lock, &hlock, subclass);

		}

		return;

	}



	raw_local_irq_save(flags);

	check_flags(flags);

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