Re: [patch] staging: ion: use two separate locks for heaps and clients in ion_device

[YiPing Xu <xuyiping@hisilicon.com>]

On 2016/10/5 2:02, Laura Abbott wrote:
> On 09/30/2016 01:18 AM, Xu YiPing wrote:
>> ion_alloc may get into slow path to get free page,
>> the call stack:
>>
>> __alloc_pages_slowpath
>> ion_page_pool_alloc_pages
>> alloc_buffer_page
>> ion_system_heap_allocate
>> ion_buffer_create  <-- hold ion_device->lock
>> ion_alloc
>>
>> after that, kernel invokes low-memory killer to kill some apps in
>> order to free memory in android system. However, sometimes, the
>> killing is blocked,
>> the app's call stack:
>>
>> rwsem_down_write_failed
>> down_write
>> ion_client_destroy
>> ion_release
>> fput
>> do_signal
>>
>> the killing is blocked because ion_device->lock is held by ion_alloc.
>>
>> ion_alloc hold the lock for accessing the heaps list,
>> ion_destroy_client hold the lock for accessing the clients list.
>>
>> so, we can use two separate locks for heaps and clients, to avoid the
>> unnecessary race.
>>
>
> I've reviewed this and it looks okay at first pass but I don't want it
> applied just yet. Ion locking is a bit of a mess and has been added

yes, and now "debugfs_mutex" and "ion_root_client" is redundant, after 
commit 49d200deaa680501f19a247b1fffb29301e51d2b and 
9fd4dcece43a53e5a9e65a973df5693702ee6401.

> once piece at a time. It needs a fundamental review. There will be Ion
> discussions at plumbers at the end of October. Let's come back to this
> after plumbers.
>
>> Signed-off-by: Xu YiPing <xuyiping@hisilicon.com>
>> ---
>>  drivers/staging/android/ion/ion.c | 37
>> ++++++++++++++++++++-----------------
>>  1 file changed, 20 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/staging/android/ion/ion.c
>> b/drivers/staging/android/ion/ion.c
>> index a2cf93b..331ad0f 100644
>> --- a/drivers/staging/android/ion/ion.c
>> +++ b/drivers/staging/android/ion/ion.c
>> @@ -46,7 +46,8 @@
>>   * @dev:        the actual misc device
>>   * @buffers:        an rb tree of all the existing buffers
>>   * @buffer_lock:    lock protecting the tree of buffers
>> - * @lock:        rwsem protecting the tree of heaps and clients
>> + * @client_lock:    rwsem protecting the tree of clients
>> + * @heap_lock:        rwsem protecting the tree of heaps
>>   * @heaps:        list of all the heaps in the system
>>   * @user_clients:    list of all the clients created from userspace
>>   */
>> @@ -54,7 +55,8 @@ struct ion_device {
>>      struct miscdevice dev;
>>      struct rb_root buffers;
>>      struct mutex buffer_lock;
>> -    struct rw_semaphore lock;
>> +    struct rw_semaphore client_lock;
>> +    struct rw_semaphore heap_lock;
>>      struct plist_head heaps;
>>      long (*custom_ioctl)(struct ion_client *client, unsigned int cmd,
>>                   unsigned long arg);
>> @@ -146,7 +148,7 @@ static inline void ion_buffer_page_clean(struct
>> page **page)
>>      *page = (struct page *)((unsigned long)(*page) & ~(1UL));
>>  }
>>
>> -/* this function should only be called while dev->lock is held */
>> +/* this function should only be called while dev->heap_lock is held */
>>  static void ion_buffer_add(struct ion_device *dev,
>>                 struct ion_buffer *buffer)
>>  {
>> @@ -172,7 +174,7 @@ static void ion_buffer_add(struct ion_device *dev,
>>      rb_insert_color(&buffer->node, &dev->buffers);
>>  }
>>
>> -/* this function should only be called while dev->lock is held */
>> +/* this function should only be called while dev->heap_lock is held */
>>  static struct ion_buffer *ion_buffer_create(struct ion_heap *heap,
>>                       struct ion_device *dev,
>>                       unsigned long len,
>> @@ -511,7 +513,7 @@ struct ion_handle *ion_alloc(struct ion_client
>> *client, size_t len,
>>      if (!len)
>>          return ERR_PTR(-EINVAL);
>>
>> -    down_read(&dev->lock);
>> +    down_read(&dev->heap_lock);
>>      plist_for_each_entry(heap, &dev->heaps, node) {
>>          /* if the caller didn't specify this heap id */
>>          if (!((1 << heap->id) & heap_id_mask))
>> @@ -520,7 +522,7 @@ struct ion_handle *ion_alloc(struct ion_client
>> *client, size_t len,
>>          if (!IS_ERR(buffer))
>>              break;
>>      }
>> -    up_read(&dev->lock);
>> +    up_read(&dev->heap_lock);
>>
>>      if (buffer == NULL)
>>          return ERR_PTR(-ENODEV);
>> @@ -713,7 +715,7 @@ static int is_client_alive(struct ion_client *client)
>>      node = ion_root_client->rb_node;
>>      dev = container_of(ion_root_client, struct ion_device, clients);
>>
>> -    down_read(&dev->lock);
>> +    down_read(&dev->client_lock);
>>      while (node) {
>>          tmp = rb_entry(node, struct ion_client, node);
>>          if (client < tmp) {
>> @@ -721,12 +723,12 @@ static int is_client_alive(struct ion_client
>> *client)
>>          } else if (client > tmp) {
>>              node = node->rb_right;
>>          } else {
>> -            up_read(&dev->lock);
>> +            up_read(&dev->client_lock);
>>              return 1;
>>          }
>>      }
>>
>> -    up_read(&dev->lock);
>> +    up_read(&dev->client_lock);
>>      return 0;
>>  }
>>
>> @@ -841,12 +843,12 @@ struct ion_client *ion_client_create(struct
>> ion_device *dev,
>>      if (!client->name)
>>          goto err_free_client;
>>
>> -    down_write(&dev->lock);
>> +    down_write(&dev->client_lock);
>>      client->display_serial = ion_get_client_serial(&dev->clients, name);
>>      client->display_name = kasprintf(
>>          GFP_KERNEL, "%s-%d", name, client->display_serial);
>>      if (!client->display_name) {
>> -        up_write(&dev->lock);
>> +        up_write(&dev->client_lock);
>>          goto err_free_client_name;
>>      }
>>      p = &dev->clients.rb_node;
>> @@ -873,7 +875,7 @@ struct ion_client *ion_client_create(struct
>> ion_device *dev,
>>              path, client->display_name);
>>      }
>>
>> -    up_write(&dev->lock);
>> +    up_write(&dev->client_lock);
>>
>>      return client;
>>
>> @@ -903,12 +905,12 @@ void ion_client_destroy(struct ion_client *client)
>>
>>      idr_destroy(&client->idr);
>>
>> -    down_write(&dev->lock);
>> +    down_write(&dev->client_lock);
>>      if (client->task)
>>          put_task_struct(client->task);
>>      rb_erase(&client->node, &dev->clients);
>>      debugfs_remove_recursive(client->debug_root);
>> -    up_write(&dev->lock);
>> +    up_write(&dev->client_lock);
>>
>>      kfree(client->display_name);
>>      kfree(client->name);
>> @@ -1603,7 +1605,7 @@ void ion_device_add_heap(struct ion_device *dev,
>> struct ion_heap *heap)
>>          ion_heap_init_shrinker(heap);
>>
>>      heap->dev = dev;
>> -    down_write(&dev->lock);
>> +    down_write(&dev->heap_lock);
>>      /*
>>       * use negative heap->id to reverse the priority -- when traversing
>>       * the list later attempt higher id numbers first
>> @@ -1638,7 +1640,7 @@ void ion_device_add_heap(struct ion_device *dev,
>> struct ion_heap *heap)
>>          }
>>      }
>>
>> -    up_write(&dev->lock);
>> +    up_write(&dev->heap_lock);
>>  }
>>  EXPORT_SYMBOL(ion_device_add_heap);
>>
>> @@ -1685,7 +1687,8 @@ debugfs_done:
>>      idev->custom_ioctl = custom_ioctl;
>>      idev->buffers = RB_ROOT;
>>      mutex_init(&idev->buffer_lock);
>> -    init_rwsem(&idev->lock);
>> +    init_rwsem(&idev->client_lock);
>> +    init_rwsem(&idev->heap_lock);
>>      plist_head_init(&idev->heaps);
>>      idev->clients = RB_ROOT;
>>      ion_root_client = &idev->clients;
>> --
>> 2.7.4
>>
>
>
> .
>