Re: [PATCH 1/3] drm/ttm: add ttm_bo_is_reserved

[Maarten Lankhorst <maarten.lankhorst@canonical.com>]

Op 25-10-12 09:42, Thomas Hellstrom schreef:
> On 10/12/2012 04:58 PM, Maarten Lankhorst wrote:
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
>> ---
>>   drivers/gpu/drm/ttm/ttm_bo.c |   12 ++++++------
>>   include/drm/ttm/ttm_bo_api.h |   14 ++++++++++++++
>>   2 files changed, 20 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>> index be1148e..d9d8541 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>> @@ -161,9 +161,9 @@ int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo, bool interruptible)
>>   {
>>       if (interruptible) {
>>           return wait_event_interruptible(bo->event_queue,
>> -                           atomic_read(&bo->reserved) == 0);
>> +                           !ttm_bo_is_reserved(bo));
>>       } else {
>> -        wait_event(bo->event_queue, atomic_read(&bo->reserved) == 0);
>> +        wait_event(bo->event_queue, !ttm_bo_is_reserved(bo));
>>           return 0;
>>       }
>>   }
>> @@ -174,7 +174,7 @@ void ttm_bo_add_to_lru(struct ttm_buffer_object *bo)
>>       struct ttm_bo_device *bdev = bo->bdev;
>>       struct ttm_mem_type_manager *man;
>>   -    BUG_ON(!atomic_read(&bo->reserved));
>> +    BUG_ON(!ttm_bo_is_reserved(bo));
>>         if (!(bo->mem.placement & TTM_PL_FLAG_NO_EVICT)) {
>>   @@ -748,7 +748,7 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo, bool interruptible,
>>           goto out;
>>       }
>>   -    BUG_ON(!atomic_read(&bo->reserved));
>> +    BUG_ON(!ttm_bo_is_reserved(bo));
>>         evict_mem = bo->mem;
>>       evict_mem.mm_node = NULL;
>> @@ -1058,7 +1058,7 @@ int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
>>       struct ttm_mem_reg mem;
>>       struct ttm_bo_device *bdev = bo->bdev;
>>   -    BUG_ON(!atomic_read(&bo->reserved));
>> +    BUG_ON(!ttm_bo_is_reserved(bo));
>>         /*
>>        * FIXME: It's possible to pipeline buffer moves.
>> @@ -1115,7 +1115,7 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
>>   {
>>       int ret;
>>   -    BUG_ON(!atomic_read(&bo->reserved));
>> +    BUG_ON(!ttm_bo_is_reserved(bo));
>>       /* Check that range is valid */
>>       if (placement->lpfn || placement->fpfn)
>>           if (placement->fpfn > placement->lpfn ||
>> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
>> index 9654451..1d71f6b 100644
>> --- a/include/drm/ttm/ttm_bo_api.h
>> +++ b/include/drm/ttm/ttm_bo_api.h
>> @@ -705,4 +705,18 @@ extern ssize_t ttm_bo_io(struct ttm_bo_device *bdev, struct file *filp,
>>     extern void ttm_bo_swapout_all(struct ttm_bo_device *bdev);
>>   +/**
>> + * ttm_bo_is_reserved - return an indication if a ttm buffer object is reserved
>> + *
>> + * @bo:     The buffer object to check.
>> + *
>> + * This function returns an indication if a bo is reserved or not, and should
>> + * only be used to print an error when it is not from incorrect api usage, since
>> + * there's no guarantee that it is the caller that is holding the reservation.
>> + */
>> +static inline bool ttm_bo_is_reserved(struct ttm_buffer_object *bo)
>> +{
>> +    return atomic_read(&bo->reserved);
>> +}
>> +
>>   #endif
> This looks good, although for clarity we should add in the comments that
> if the caller is holding the reservation, the function is guaranteed to return true.
>
> Otherwise
> Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>

Unless you use lockdep, you can't say with 100% certainty if the CALLER is holding it or not. :-)
But lockdep can actually check if that's the case with lockdep_is_held(&ttm->reservation_lock);
which iterates over all locks held by the current task.

~Maarten

Updated version with a comment about return value in ttm_bo_is_reserved:

drm/ttm: Add ttm_bo_is_reserved function
    
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 2b3f69b..82e2633 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -162,9 +162,9 @@ int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo, bool interruptible)
 {
 	if (interruptible) {
 		return wait_event_interruptible(bo->event_queue,
-					       atomic_read(&bo->reserved) == 0);
+					       !ttm_bo_is_reserved(bo));
 	} else {
-		wait_event(bo->event_queue, atomic_read(&bo->reserved) == 0);
+		wait_event(bo->event_queue, !ttm_bo_is_reserved(bo));
 		return 0;
 	}
 }
@@ -175,7 +175,7 @@ void ttm_bo_add_to_lru(struct ttm_buffer_object *bo)
 	struct ttm_bo_device *bdev = bo->bdev;
 	struct ttm_mem_type_manager *man;
 
-	BUG_ON(!atomic_read(&bo->reserved));
+	BUG_ON(!ttm_bo_is_reserved(bo));
 
 	if (!(bo->mem.placement & TTM_PL_FLAG_NO_EVICT)) {
 
@@ -756,7 +756,7 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo, bool interruptible,
 		goto out;
 	}
 
-	BUG_ON(!atomic_read(&bo->reserved));
+	BUG_ON(!ttm_bo_is_reserved(bo));
 
 	evict_mem = bo->mem;
 	evict_mem.mm_node = NULL;
@@ -1063,7 +1063,7 @@ int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
 	struct ttm_mem_reg mem;
 	struct ttm_bo_device *bdev = bo->bdev;
 
-	BUG_ON(!atomic_read(&bo->reserved));
+	BUG_ON(!ttm_bo_is_reserved(bo));
 
 	/*
 	 * FIXME: It's possible to pipeline buffer moves.
@@ -1120,7 +1120,7 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
 {
 	int ret;
 
-	BUG_ON(!atomic_read(&bo->reserved));
+	BUG_ON(!ttm_bo_is_reserved(bo));
 	/* Check that range is valid */
 	if (placement->lpfn || placement->fpfn)
 		if (placement->fpfn > placement->lpfn ||
diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index 850424f..7a5b574 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -737,4 +737,20 @@ extern ssize_t ttm_bo_io(struct ttm_bo_device *bdev, struct file *filp,
 
 extern void ttm_bo_swapout_all(struct ttm_bo_device *bdev);
 
+/**
+ * ttm_bo_is_reserved - return an indication if a ttm buffer object is reserved
+ *
+ * @bo:     The buffer object to check.
+ *
+ * This function returns an indication if a bo is reserved or not, and should
+ * only be used to print an error when it is not from incorrect api usage, since
+ * there's no guarantee that it is the caller that is holding the reservation.
+ *
+ * Returns true if reserved, false if unreserved.
+ */
+static inline bool ttm_bo_is_reserved(struct ttm_buffer_object *bo)
+{
+	return atomic_read(&bo->reserved);
+}
+
 #endif