[RFC PATCH 12/13] drm/ttm: Use fault-injection to test error paths

[Thomas Hellström]

Use fault-injection to test partial TTM swapout and interrupted swapin.

Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
---
 drivers/gpu/drm/Kconfig        | 10 ++++++++++
 drivers/gpu/drm/ttm/ttm_pool.c | 17 ++++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index dc0f94f02a82..1c89834f66b4 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -201,6 +201,16 @@ config DRM_TTM
 	  GPU memory types. Will be enabled automatically if a device driver
 	  uses it.
 
+config DRM_TTM_SHRINK_FAULT_INJECT
+        bool "Enable fault injection during TTM shrinking"
+        depends on DRM_TTM
+	default n
+	help
+	  Inject recoverable failures during TTM shrinking and recovery of
+	  shrunken objects. For DRM driver developers only.
+
+	  If in doubt, choose N.
+
 config DRM_BUDDY
 	tristate
 	depends on DRM
diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index a01fa7f09005..21939fc4fd39 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -449,6 +449,7 @@ static bool ttm_pool_restore_valid(const struct ttm_pool_tt_restore *restore)
 static int ttm_pool_swapin(struct ttm_pool_tt_restore *restore,
 			   struct ttm_operation_ctx *ctx)
 {
+	static unsigned long __maybe_unused swappedin;
 	unsigned int i, nr = 1 << restore->order;
 	int ret = 0;
 
@@ -464,6 +465,13 @@ static int ttm_pool_swapin(struct ttm_pool_tt_restore *restore,
 			if (swap.val == 0)
 				continue;
 
+			if (IS_ENABLED(CONFIG_DRM_TTM_SHRINK_FAULT_INJECT) &&
+			    ctx->interruptible &&
+			    ++swappedin % 100 == 0) {
+				ret = -EINTR;
+				break;
+			}
+
 			ret = swap_copy_folio(swap, restore->first_page[i], 0,
 					      ctx->interruptible);
 			if (ret)
@@ -851,7 +859,14 @@ long ttm_pool_shrink_tt(struct ttm_pool *pool, struct ttm_tt *ttm)
 	if (purge)
 		return shrunken;
 
-	for (i = 0; i < ttm->num_pages; ++i) {
+	num_pages = ttm->num_pages;
+
+	/* Pretend doing fault injection by shrinking only half of the pages. */
+
+	if (IS_ENABLED(CONFIG_DRM_TTM_SHRINK_FAULT_INJECT))
+		num_pages = DIV_ROUND_UP(num_pages, 2);
+
+	for (i = 0; i < num_pages; ++i) {
 		page = ttm->pages[i];
 		if (unlikely(!page))
 			continue;
-- 
2.34.1