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drm/amdgpu: drop retry loop in amdgpu_hmm_range_get_pages

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commit 342981fff32802a819d6fc7cf3c9fedf9f3d9d60 upstream.

Since commit c08972f55594 ("drm/amdgpu: fix amdgpu_hmm_range_get_pages")
moved mmu_interval_read_begin() out of the per-chunk loop, the
captured notifier_seq is no longer refreshed across retries. As a
result, the existing -EBUSY retry path can never make progress:

  hmm_range_fault() returns -EBUSY only when
  mmu_interval_check_retry(notifier, notifier_seq) reports that the
  sequence is stale. Once the sequence has advanced, the stored seq
  will never match again, so every subsequent call within the same
  invocation returns -EBUSY immediately.

The "goto retry" therefore degenerates into a busy spin that simply
burns CPU for the full HMM_RANGE_DEFAULT_TIMEOUT (~1s) window before
finally bailing out with -EAGAIN. This is pure latency with no chance
of recovery, and it actively hurts the KFD userptr stack: the caller
ends up blocked for a second while holding mmap_lock, only to return
-EAGAIN to the restore worker (or to userspace) which would have
re-driven the operation immediately anyway.

Drop the retry/timeout entirely and let -EBUSY propagate straight to
out_free_pfns, where it is already translated to -EAGAIN. Recovery is
handled at a higher level: the KFD restore_userptr_worker reschedules
itself, and the userptr ioctl path returns -EAGAIN to userspace.

No functional regression: the previous behaviour on -EBUSY was already
to fail with -EAGAIN after a 1s stall; we just skip the stall.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Honglei Huang <honghuan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Honglei Huang 2026-05-29 10:23:17 +08:00 • committed by Greg Kroah-Hartman
commit ce3fb4b971
1 changed files with 1 additions and 8 deletions
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9
drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c
View file

@ -174,7 +174,6 @@ int amdgpu_hmm_range_get_pages(struct mmu_interval_notifier *notifier,
const u64 max_bytes = SZ_2G;
struct hmm_range *hmm_range = &range->hmm_range;
unsigned long timeout;
unsigned long *pfns;
unsigned long end;
int r;
@ -201,15 +200,9 @@ int amdgpu_hmm_range_get_pages(struct mmu_interval_notifier *notifier,
pr_debug("hmm range: start = 0x%lx, end = 0x%lx",
hmm_range->start, hmm_range->end);
timeout = jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
retry:
r = hmm_range_fault(hmm_range);
if (unlikely(r)) {
if (r == -EBUSY && !time_after(jiffies, timeout))
goto retry;
if (unlikely(r))
goto out_free_pfns;
}
if (hmm_range->end == end)
break;