Re: [PATCH 1/3] drm/i915: Fix negative remaining time after retire requests

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On 11/16/2022 12:25 PM, 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.


Thanks for the detailed comment, indeed we were not accounting for the return value of dma_fence_wait_timeout()

Acked-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>


Thanks,

Nirmoy


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 */
+				}
+
  				/* 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;
  }



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