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authorThomas Hellstrom <thellstrom@vmware.com>2010-11-11 10:04:53 +0100
committerDave Airlie <airlied@redhat.com>2010-11-18 15:00:42 +1000
commit95ccb0f3bdc4438bf470c25450e6a8a6090ca253 (patch)
treea4a55496a9483ddf43d8bd72c149341536628874 /drivers/gpu/drm/ttm/ttm_bo.c
parent9a03d3487abe89e3650bb2533c5d909143955499 (diff)
drm/ttm: Fix up a theoretical deadlock
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>
Diffstat (limited to 'drivers/gpu/drm/ttm/ttm_bo.c')
-rw-r--r--drivers/gpu/drm/ttm/ttm_bo.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 3ca77dc0391..148a322d8f5 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -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 {