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drm/ttm: remove lru_lock around ttm_bo_reserve
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There should no longer be assumptions that reserve will always succeed
with the lru lock held, so we can safely break the whole atomic
reserve/lru thing. As a bonus this fixes most lockdep annotations for
reservations.

Signed-off-by: Maarten Lankhorst <[email protected]>
Reviewed-by: Jerome Glisse <[email protected]>
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Maarten Lankhorst committed Jan 15, 2013
1 parent 979ee29 commit 63d0a41
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Showing 3 changed files with 40 additions and 35 deletions.
54 changes: 35 additions & 19 deletions drivers/gpu/drm/ttm/ttm_bo.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -213,14 +213,13 @@ int ttm_bo_del_from_lru(struct ttm_buffer_object *bo)
return put_count;
}

int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
int ttm_bo_reserve_nolru(struct ttm_buffer_object *bo,
bool interruptible,
bool no_wait, bool use_sequence, uint32_t sequence)
{
struct ttm_bo_global *glob = bo->glob;
int ret;

while (unlikely(atomic_read(&bo->reserved) != 0)) {
while (unlikely(atomic_xchg(&bo->reserved, 1) != 0)) {
/**
* Deadlock avoidance for multi-bo reserving.
*/
Expand All @@ -241,26 +240,36 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
if (no_wait)
return -EBUSY;

spin_unlock(&glob->lru_lock);
ret = ttm_bo_wait_unreserved(bo, interruptible);
spin_lock(&glob->lru_lock);

if (unlikely(ret))
return ret;
}

atomic_set(&bo->reserved, 1);
if (use_sequence) {
bool wake_up = false;
/**
* Wake up waiters that may need to recheck for deadlock,
* if we decreased the sequence number.
*/
if (unlikely((bo->val_seq - sequence < (1 << 31))
|| !bo->seq_valid))
wake_up_all(&bo->event_queue);
wake_up = true;

/*
* In the worst case with memory ordering these values can be
* seen in the wrong order. However since we call wake_up_all
* in that case, this will hopefully not pose a problem,
* and the worst case would only cause someone to accidentally
* hit -EAGAIN in ttm_bo_reserve when they see old value of
* val_seq. However this would only happen if seq_valid was
* written before val_seq was, and just means some slightly
* increased cpu usage
*/
bo->val_seq = sequence;
bo->seq_valid = true;
if (wake_up)
wake_up_all(&bo->event_queue);
} else {
bo->seq_valid = false;
}
Expand Down Expand Up @@ -289,14 +298,14 @@ int ttm_bo_reserve(struct ttm_buffer_object *bo,
int put_count = 0;
int ret;

spin_lock(&glob->lru_lock);
ret = ttm_bo_reserve_locked(bo, interruptible, no_wait, use_sequence,
sequence);
if (likely(ret == 0))
ret = ttm_bo_reserve_nolru(bo, interruptible, no_wait, use_sequence,
sequence);
if (likely(ret == 0)) {
spin_lock(&glob->lru_lock);
put_count = ttm_bo_del_from_lru(bo);
spin_unlock(&glob->lru_lock);

ttm_bo_list_ref_sub(bo, put_count, true);
spin_unlock(&glob->lru_lock);
ttm_bo_list_ref_sub(bo, put_count, true);
}

return ret;
}
Expand Down Expand Up @@ -510,7 +519,7 @@ static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)
int ret;

spin_lock(&glob->lru_lock);
ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
ret = ttm_bo_reserve_nolru(bo, false, true, false, 0);

spin_lock(&bdev->fence_lock);
(void) ttm_bo_wait(bo, false, false, true);
Expand Down Expand Up @@ -603,7 +612,7 @@ static int ttm_bo_cleanup_refs_and_unlock(struct ttm_buffer_object *bo,
return ret;

spin_lock(&glob->lru_lock);
ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
ret = ttm_bo_reserve_nolru(bo, false, true, false, 0);

/*
* We raced, and lost, someone else holds the reservation now,
Expand Down Expand Up @@ -667,7 +676,14 @@ static int ttm_bo_delayed_delete(struct ttm_bo_device *bdev, bool remove_all)
kref_get(&nentry->list_kref);
}

ret = ttm_bo_reserve_locked(entry, false, !remove_all, false, 0);
ret = ttm_bo_reserve_nolru(entry, false, true, false, 0);
if (remove_all && ret) {
spin_unlock(&glob->lru_lock);
ret = ttm_bo_reserve_nolru(entry, false, false,
false, 0);
spin_lock(&glob->lru_lock);
}

if (!ret)
ret = ttm_bo_cleanup_refs_and_unlock(entry, false,
!remove_all);
Expand Down Expand Up @@ -815,7 +831,7 @@ static int ttm_mem_evict_first(struct ttm_bo_device *bdev,

spin_lock(&glob->lru_lock);
list_for_each_entry(bo, &man->lru, lru) {
ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
ret = ttm_bo_reserve_nolru(bo, false, true, false, 0);
if (!ret)
break;
}
Expand Down Expand Up @@ -1796,7 +1812,7 @@ static int ttm_bo_swapout(struct ttm_mem_shrink *shrink)

spin_lock(&glob->lru_lock);
list_for_each_entry(bo, &glob->swap_lru, swap) {
ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
ret = ttm_bo_reserve_nolru(bo, false, true, false, 0);
if (!ret)
break;
}
Expand Down
2 changes: 1 addition & 1 deletion drivers/gpu/drm/ttm/ttm_execbuf_util.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -153,7 +153,7 @@ int ttm_eu_reserve_buffers(struct list_head *list)
struct ttm_buffer_object *bo = entry->bo;

retry_this_bo:
ret = ttm_bo_reserve_locked(bo, true, true, true, val_seq);
ret = ttm_bo_reserve_nolru(bo, true, true, true, val_seq);
switch (ret) {
case 0:
break;
Expand Down
19 changes: 4 additions & 15 deletions include/drm/ttm/ttm_bo_driver.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -790,16 +790,7 @@ extern void ttm_mem_io_unlock(struct ttm_mem_type_manager *man);
* to make room for a buffer already reserved. (Buffers are reserved before
* they are evicted). The following algorithm prevents such deadlocks from
* occurring:
* 1) Buffers are reserved with the lru spinlock held. Upon successful
* reservation they are removed from the lru list. This stops a reserved buffer
* from being evicted. However the lru spinlock is released between the time
* a buffer is selected for eviction and the time it is reserved.
* Therefore a check is made when a buffer is reserved for eviction, that it
* is still the first buffer in the lru list, before it is removed from the
* list. @check_lru == 1 forces this check. If it fails, the function returns
* -EINVAL, and the caller should then choose a new buffer to evict and repeat
* the procedure.
* 2) Processes attempting to reserve multiple buffers other than for eviction,
* Processes attempting to reserve multiple buffers other than for eviction,
* (typically execbuf), should first obtain a unique 32-bit
* validation sequence number,
* and call this function with @use_sequence == 1 and @sequence == the unique
Expand Down Expand Up @@ -832,17 +823,15 @@ extern int ttm_bo_reserve(struct ttm_buffer_object *bo,


/**
* ttm_bo_reserve_locked:
* ttm_bo_reserve_nolru:
*
* @bo: A pointer to a struct ttm_buffer_object.
* @interruptible: Sleep interruptible if waiting.
* @no_wait: Don't sleep while trying to reserve, rather return -EBUSY.
* @use_sequence: If @bo is already reserved, Only sleep waiting for
* it to become unreserved if @sequence < (@bo)->sequence.
*
* Must be called with struct ttm_bo_global::lru_lock held,
* and will not remove reserved buffers from the lru lists.
* The function may release the LRU spinlock if it needs to sleep.
* Will not remove reserved buffers from the lru lists.
* Otherwise identical to ttm_bo_reserve.
*
* Returns:
Expand All @@ -855,7 +844,7 @@ extern int ttm_bo_reserve(struct ttm_buffer_object *bo,
* -EDEADLK: Bo already reserved using @sequence. This error code will only
* be returned if @use_sequence is set to true.
*/
extern int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
extern int ttm_bo_reserve_nolru(struct ttm_buffer_object *bo,
bool interruptible,
bool no_wait, bool use_sequence,
uint32_t sequence);
Expand Down

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