4.4-stable review patch. If anyone has any objections, please let me know.
------------------
[ Upstream commit c74f7e8281add80bdfa0ad2998b8df287b13df73 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/hwtracing/stm/core.c | 38 +++++++++++++++++++++++++++--------- drivers/hwtracing/stm/stm.h | 1 + 2 files changed, 30 insertions(+), 9 deletions(-)
diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c index 92ab51aa8a74..f286de2e86af 100644 --- a/drivers/hwtracing/stm/core.c +++ b/drivers/hwtracing/stm/core.c @@ -647,6 +647,7 @@ 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);
@@ -677,11 +678,11 @@ 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);
@@ -700,6 +701,17 @@ 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 @@ -716,6 +728,7 @@ 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);
@@ -725,6 +738,7 @@ 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) { @@ -762,6 +776,7 @@ 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);
@@ -770,6 +785,7 @@ 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; } @@ -782,13 +798,20 @@ 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)) { @@ -797,13 +820,13 @@ 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); }
/** @@ -825,12 +848,9 @@ 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); diff --git a/drivers/hwtracing/stm/stm.h b/drivers/hwtracing/stm/stm.h index 95ece0292c99..97ee02241440 100644 --- a/drivers/hwtracing/stm/stm.h +++ b/drivers/hwtracing/stm/stm.h @@ -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 */