[PATCH 1/2] drm/xe/sa: make suballocator waits uninterruptible

[Matthew Auld <matthew.auld@intel.com>]

Large BO clears and copies in xe_migrate_clear() and xe_migrate_copy()
are split into multiple passes, each needing a batchbuffer from the
fixed size kernel bb pool. Once the pool fills up, __xe_sa_bo_new()
waits interruptibly for space, so a pending signal (e.g. Xorg's 5ms
SIGALRM smart-scheduler timer) makes it fail mid-loop with -ERESTARTSYS.
The partial progress is then thrown away and the restarted ioctl starts
again from byte 0, including the memory allocation, which can livelock
if the signal arrives faster than the whole operation completes. In the
shrinker path the same error also aborts the shrinker walk, even though
ctx->interruptible is false.

Being interruptible here doesn't seem to buy much anyway: on error
the loop already waits uninterruptibly for all submitted passes before
returning. So just make the suballocator waits uninterruptible, matching
amdgpu and radeon. The other users (page reclaim from a kworker, and the
GuC buffer cache) shouldn't really see any meaningful change.

Assisted-by: LLM
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/9644
Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <stable@vger.kernel.org> # v6.12+
---
 drivers/gpu/drm/xe/xe_sa.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_sa.c b/drivers/gpu/drm/xe/xe_sa.c
index f32045f40b7a..d9c2b28b08c2 100644
--- a/drivers/gpu/drm/xe/xe_sa.c
+++ b/drivers/gpu/drm/xe/xe_sa.c
@@ -165,7 +165,8 @@ void xe_sa_bo_sync_shadow(struct drm_suballoc *sa_bo)
  * @size: number of bytes we want to suballocate
  * @gfp: gfp flags used for memory allocation. Typically GFP_KERNEL.
  *
- * Try to make a suballocation of size @size.
+ * Try to make a suballocation of size @size. Any waits for space are
+ * uninterruptible.
  *
  * Return: a &drm_suballoc, or an ERR_PTR.
  */
@@ -178,7 +179,7 @@ struct drm_suballoc *__xe_sa_bo_new(struct xe_sa_manager *sa_manager, u32 size,
 	if (size > sa_manager->base.size)
 		return ERR_PTR(-ENOBUFS);
 
-	return drm_suballoc_new(&sa_manager->base, size, gfp, true, 0);
+	return drm_suballoc_new(&sa_manager->base, size, gfp, false, 0);
 }
 
 /**
-- 
2.56.0