Commit d74185ed authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Ingo Molnar
Browse files

markers: fix unregister bug and reenter bug 



unregister bug:

codes using makers are typically calling marker_probe_unregister()
and then destroying the data that marker_probe_func needs(or
unloading this module). This is bug when the corresponding
marker_probe_func is still running(on other cpus),
it is using the destroying/ed data.

we should call synchronize_sched() after marker_update_probes().

reenter bug:

marker_probe_register(), marker_probe_unregister() and
marker_probe_unregister_private_data() are not reentrant safe
functions. these 3 functions release markers_mutex and then
require it again and do "entry->oldptr = old; ...", but entry->oldptr
maybe is using now for these 3 functions may reenter when markers_mutex
is released.

we use synchronize_sched() instead of call_rcu_sched() to fix
this bug. actually we can do:
"
if (entry->rcu_pending)
		rcu_barrier_sched();
"
after require markers_mutex again. but synchronize_sched()
is better and simpler. For these 3 functions are not critical path.

Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent ac2b86fd

kernel/marker.c

+6 −46
Original line number Diff line number Diff line
@@ -60,9 +60,6 @@ struct marker_entry { 
	struct marker_probe_closure single;

	struct marker_probe_closure *multi;

	int refcount;	/* Number of times armed. 0 if disarmed. */

	struct rcu_head rcu;

	void *oldptr;

	unsigned char rcu_pending:1;

	unsigned char ptype:1;

	char name[0];	/* Contains name'\0'format'\0' */

};
@@ -199,16 +196,6 @@ void marker_probe_cb_noarg(const struct marker *mdata, void *call_private, ...) 
}

EXPORT_SYMBOL_GPL(marker_probe_cb_noarg);



static void free_old_closure(struct rcu_head *head)

{

	struct marker_entry *entry = container_of(head,

		struct marker_entry, rcu);

	kfree(entry->oldptr);

	/* Make sure we free the data before setting the pending flag to 0 */

	smp_wmb();

	entry->rcu_pending = 0;

}



static void debug_print_probes(struct marker_entry *entry)

{

	int i;
@@ -417,7 +404,6 @@ static struct marker_entry *add_marker(const char *name, const char *format) 
	e->multi = NULL;

	e->ptype = 0;

	e->refcount = 0;

	e->rcu_pending = 0;

	hlist_add_head(&e->hlist, head);

	return e;

}
@@ -447,9 +433,6 @@ static int remove_marker(const char *name) 
	if (e->single.func != __mark_empty_function)

		return -EBUSY;

	hlist_del(&e->hlist);

	/* Make sure the call_rcu has been executed */

	if (e->rcu_pending)

		rcu_barrier_sched();

	kfree(e);

	return 0;

}
@@ -479,12 +462,8 @@ static int marker_set_format(struct marker_entry **entry, const char *format) 
	e->multi = (*entry)->multi;

	e->ptype = (*entry)->ptype;

	e->refcount = (*entry)->refcount;

	e->rcu_pending = 0;

	hlist_add_before(&e->hlist, &(*entry)->hlist);

	hlist_del(&(*entry)->hlist);

	/* Make sure the call_rcu has been executed */

	if ((*entry)->rcu_pending)

		rcu_barrier_sched();

	kfree(*entry);

	*entry = e;

	trace_mark(core_marker_format, "name %s format %s",
@@ -658,12 +637,6 @@ int marker_probe_register(const char *name, const char *format, 
			goto end;

		}

	}

	/*

	 * If we detect that a call_rcu is pending for this marker,

	 * make sure it's executed now.

	 */

	if (entry->rcu_pending)

		rcu_barrier_sched();

	old = marker_entry_add_probe(entry, probe, probe_private);

	if (IS_ERR(old)) {

		ret = PTR_ERR(old);
@@ -671,14 +644,11 @@ int marker_probe_register(const char *name, const char *format, 
	}

	mutex_unlock(&markers_mutex);

	marker_update_probes();		/* may update entry */

	synchronize_sched();

	kfree(old);

	mutex_lock(&markers_mutex);

	entry = get_marker(name);

	WARN_ON(!entry);

	entry->oldptr = old;

	entry->rcu_pending = 1;

	/* write rcu_pending before calling the RCU callback */

	smp_wmb();

	call_rcu_sched(&entry->rcu, free_old_closure);

end:

	mutex_unlock(&markers_mutex);

	return ret;
@@ -708,20 +678,15 @@ int marker_probe_unregister(const char *name, 
	entry = get_marker(name);

	if (!entry)

		goto end;

	if (entry->rcu_pending)

		rcu_barrier_sched();

	old = marker_entry_remove_probe(entry, probe, probe_private);

	mutex_unlock(&markers_mutex);

	marker_update_probes();		/* may update entry */

	synchronize_sched();

	kfree(old);

	mutex_lock(&markers_mutex);

	entry = get_marker(name);

	if (!entry)

		goto end;

	entry->oldptr = old;

	entry->rcu_pending = 1;

	/* write rcu_pending before calling the RCU callback */

	smp_wmb();

	call_rcu_sched(&entry->rcu, free_old_closure);

	remove_marker(name);	/* Ignore busy error message */

	ret = 0;

end:
@@ -787,19 +752,14 @@ int marker_probe_unregister_private_data(marker_probe_func *probe, 
		ret = -ENOENT;

		goto end;

	}

	if (entry->rcu_pending)

		rcu_barrier_sched();

	old = marker_entry_remove_probe(entry, NULL, probe_private);

	mutex_unlock(&markers_mutex);

	marker_update_probes();		/* may update entry */

	synchronize_sched();

	kfree(old);

	mutex_lock(&markers_mutex);

	entry = get_marker_from_private_data(probe, probe_private);

	WARN_ON(!entry);

	entry->oldptr = old;

	entry->rcu_pending = 1;

	/* write rcu_pending before calling the RCU callback */

	smp_wmb();

	call_rcu_sched(&entry->rcu, free_old_closure);

	remove_marker(entry->name);	/* Ignore busy error message */

end:

	mutex_unlock(&markers_mutex);

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