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Commit c74f7e82 authored by Alexander Shishkin's avatar Alexander Shishkin Committed by Greg Kroah-Hartman
Browse files

stm class: Fix link list locking 



Currently, the list of stm_sources linked to an stm device is protected by
a spinlock, which also means that sources' .unlink() method is called under
this spinlock. However, this method may (and does) sleep, which means
trouble.

This patch slightly reworks locking around stm::link_list so that bits that
might_sleep() are called with a mutex held instead. Modification of this
list requires both mutex and spinlock to be held, while looking at the list
can be done under either mutex or spinlock.

Signed-off-by: default avatarAlexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 4c127fd1

drivers/hwtracing/stm/core.c

+29 −9
Original line number Diff line number Diff line
@@ -641,6 +641,7 @@ int stm_register_device(struct device *parent, struct stm_data *stm_data, 
	if (err)

		goto err_device;



	mutex_init(&stm->link_mutex);

	spin_lock_init(&stm->link_lock);

	INIT_LIST_HEAD(&stm->link_list);
@@ -671,11 +672,11 @@ void stm_unregister_device(struct stm_data *stm_data) 
	struct stm_source_device *src, *iter;

	int i;



	spin_lock(&stm->link_lock);

	mutex_lock(&stm->link_mutex);

	list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {

		__stm_source_link_drop(src, stm);

	}

	spin_unlock(&stm->link_lock);

	mutex_unlock(&stm->link_mutex);



	synchronize_srcu(&stm_source_srcu);
@@ -694,6 +695,17 @@ void stm_unregister_device(struct stm_data *stm_data) 
}

EXPORT_SYMBOL_GPL(stm_unregister_device);



/*

 * stm::link_list access serialization uses a spinlock and a mutex; holding

 * either of them guarantees that the list is stable; modification requires

 * holding both of them.

 *

 * Lock ordering is as follows:

 *   stm::link_mutex

 *     stm::link_lock

 *       src::link_lock

 */



/**

 * stm_source_link_add() - connect an stm_source device to an stm device

 * @src:	stm_source device
@@ -710,6 +722,7 @@ static int stm_source_link_add(struct stm_source_device *src, 
	char *id;

	int err;



	mutex_lock(&stm->link_mutex);

	spin_lock(&stm->link_lock);

	spin_lock(&src->link_lock);
@@ -719,6 +732,7 @@ static int stm_source_link_add(struct stm_source_device *src, 


	spin_unlock(&src->link_lock);

	spin_unlock(&stm->link_lock);

	mutex_unlock(&stm->link_mutex);



	id = kstrdup(src->data->name, GFP_KERNEL);

	if (id) {
@@ -756,6 +770,7 @@ static int stm_source_link_add(struct stm_source_device *src, 
	stm_put_device(stm);



fail_detach:

	mutex_lock(&stm->link_mutex);

	spin_lock(&stm->link_lock);

	spin_lock(&src->link_lock);
@@ -764,6 +779,7 @@ static int stm_source_link_add(struct stm_source_device *src, 


	spin_unlock(&src->link_lock);

	spin_unlock(&stm->link_lock);

	mutex_unlock(&stm->link_mutex);



	return err;

}
@@ -776,13 +792,20 @@ static int stm_source_link_add(struct stm_source_device *src, 
 * If @stm is @src::link, disconnect them from one another and put the

 * reference on the @stm device.

 *

 * Caller must hold stm::link_lock.

 * Caller must hold stm::link_mutex.

 */

static void __stm_source_link_drop(struct stm_source_device *src,

				   struct stm_device *stm)

{

	struct stm_device *link;



	lockdep_assert_held(&stm->link_mutex);



	if (src->data->unlink)

		src->data->unlink(src->data);



	/* for stm::link_list modification, we hold both mutex and spinlock */

	spin_lock(&stm->link_lock);

	spin_lock(&src->link_lock);

	link = srcu_dereference_check(src->link, &stm_source_srcu, 1);

	if (WARN_ON_ONCE(link != stm)) {
@@ -791,13 +814,13 @@ static void __stm_source_link_drop(struct stm_source_device *src, 
	}



	stm_output_free(link, &src->output);

	/* caller must hold stm::link_lock */

	list_del_init(&src->link_entry);

	/* matches stm_find_device() from stm_source_link_store() */

	stm_put_device(link);

	rcu_assign_pointer(src->link, NULL);



	spin_unlock(&src->link_lock);

	spin_unlock(&stm->link_lock);

}



/**
@@ -819,12 +842,9 @@ static void stm_source_link_drop(struct stm_source_device *src) 
	stm = srcu_dereference(src->link, &stm_source_srcu);



	if (stm) {

		if (src->data->unlink)

			src->data->unlink(src->data);



		spin_lock(&stm->link_lock);

		mutex_lock(&stm->link_mutex);

		__stm_source_link_drop(src, stm);

		spin_unlock(&stm->link_lock);

		mutex_unlock(&stm->link_mutex);

	}



	srcu_read_unlock(&stm_source_srcu, idx);

drivers/hwtracing/stm/stm.h

+1 −0
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ struct stm_device { 
	int			major;

	unsigned int		sw_nmasters;

	struct stm_data		*data;

	struct mutex		link_mutex;

	spinlock_t		link_lock;

	struct list_head	link_list;

	/* master allocation */