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drm/ttm: Fix up a theoretical deadlock

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A process suspended waiting for a higher sequence or no sequence to unreserve,
a bo may be beaten to the reservation by a process with a lower sequence.
In that case the first process should give up trying to reserve and
return -EAGAIN. In order for that to happen, we must wake waiting processes
when we change sequence, so that they have a chance to detect the new
sequence.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Thomas Hellstrom 2010-11-11 10:04:53 +01:00 committed by Dave Airlie
parent 9a03d3487a
commit 95ccb0f3bd
1 changed files with 11 additions and 0 deletions
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11
drivers/gpu/drm/ttm/ttm_bo.c
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@ -224,6 +224,9 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
int ret;
while (unlikely(atomic_cmpxchg(&bo->reserved, 0, 1) != 0)) {
/**
* Deadlock avoidance for multi-bo reserving.
*/
if (use_sequence && bo->seq_valid &&
(sequence - bo->val_seq < (1 << 31))) {
return -EAGAIN;
@ -241,6 +244,14 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
}
if (use_sequence) {
/**
* 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);
bo->val_seq = sequence;
bo->seq_valid = true;
} else {