[PATCH] 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
---
drivers/gpu/drm/ttm/ttm_bo.c | 11 +++
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 3ca77dc..148a322 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(>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(>event_queue);
+
bo->val_seq = sequence;
bo->seq_valid = true;
} else {
--
1.6.2.5
[PATCH] 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 thellst...@vmware.com
---
drivers/gpu/drm/ttm/ttm_bo.c | 11 +++
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 3ca77dc..148a322 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 {
--
1.6.2.5
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