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stm class: Fix link list locking

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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: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alexander Shishkin 2015-12-22 17:25:19 +02:00 committed by Greg Kroah-Hartman
parent 4c127fd16e
commit c74f7e8281
2 changed files with 30 additions and 9 deletions
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38
drivers/hwtracing/stm/core.c
View file

@ -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 @@ fail_free_output:
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 @@ fail_detach:
spin_unlock(&src->link_lock);
spin_unlock(&stm->link_lock);
mutex_unlock(&stm->link_mutex);
return err;
}
@ -776,13 +792,20 @@ fail_detach:
* 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);

1
drivers/hwtracing/stm/stm.h
View file

@ -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 */