[RFC PATCH 15/16] drm/ttm: Use fault-injection to test error paths

[Thomas Hellström]

Use fault-injection to test partial TTM swapout and interrupted swapin.
Return -EINTR for swapin to test the callers ability to handle and
restart the swapin, and on swapout perform a partial swapout to test that
the swapin and release_shrunken functionality.

Signed-off-by: Thomas Hellström <thomas.hellst...@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 1efd33411a92..a78eed9af2c1 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -202,6 +202,16 @@ 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 319998b4a325..d7c604593689 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -453,6 +453,7 @@ 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;
 
@@ -468,6 +469,13 @@ 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)
@@ -905,7 +913,14 @@ long ttm_pool_shrink_tt(struct ttm_pool *pool, struct 
ttm_tt *ttm)
        if (current_is_kswapd())
                alloc_gfp |= __GFP_NOMEMALLOC;
 
-       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