On 16.11.2022 12:25, Janusz Krzysztofik wrote:
Commit b97060a99b01 ("drm/i915/guc: Update intel_gt_wait_for_idle to work
with GuC") extended the API of intel_gt_retire_requests_timeout() with an
extra argument 'remaining_timeout', intended for passing back unconsumed
portion of requested timeout when 0 (success) is returned. However, when
request retirement happens to succeed despite an error returned by
dma_fence_wait_timeout(), the error code (a negative value) is passed back
instead of remaining time. If a user then passes that negative value
forward as requested timeout to another wait, an explicit WARN or BUG can
be triggered.
Instead of copying the value of timeout variable to *remaining_timeout
before return, update the *remaining_timeout after each DMA fence wait.
Set it to 0 on -ETIME, -EINTR or -ERESTARTSYS, and assume no time has been
consumed on other errors returned from the wait.
Fixes: b97060a99b01 ("drm/i915/guc: Update intel_gt_wait_for_idle to work with GuC")
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.15+
---
drivers/gpu/drm/i915/gt/intel_gt_requests.c | 23 ++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
index edb881d756309..ccaf2fd80625b 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
@@ -138,6 +138,9 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout,
unsigned long active_count = 0;
LIST_HEAD(free);
+ if (remaining_timeout)
+ *remaining_timeout = timeout;
+
flush_submission(gt, timeout); /* kick the ksoftirqd tasklets */
spin_lock(&timelines->lock);
list_for_each_entry_safe(tl, tn, &timelines->active_list, link) {
@@ -163,6 +166,23 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout,
timeout);
dma_fence_put(fence);
+ if (remaining_timeout) {
+ /*
+ * If we get an error here but request
+ * retirement succeeds anyway
+ * (!active_count) and we return 0, the
+ * caller may want to spend remaining
+ * time on waiting for other events.
+ */
+ if (timeout == -ETIME ||
+ timeout == -EINTR ||
+ timeout == -ERESTARTSYS)
+ *remaining_timeout = 0;
+ else if (timeout >= 0)
+ *remaining_timeout = timeout;
+ /* else assume no time consumed */
Looks correct, but the crazy semantic of dma_fence_wait_timeout does not
make it easy to understand.
Reviewed-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
Regards
Andrzej
+ }
+
/* Retirement is best effort */
if (!mutex_trylock(&tl->mutex)) {
active_count++;
@@ -196,9 +216,6 @@ out_active: spin_lock(&timelines->lock);
if (flush_submission(gt, timeout)) /* Wait, there's more! */
active_count++;
- if (remaining_timeout)
- *remaining_timeout = timeout;
-
return active_count ? timeout : 0;
}
