[PATCH v3 10/21] 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.

Cc: Christian König <christian.koe...@amd.com>
Cc: Somalapuram Amaranath <amaranath.somalapu...@amd.com>
Cc: Matthew Brost <matthew.br...@intel.com>
Cc: <dri-devel@lists.freedesktop.org>
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 026444eeb5c6..f041ef44228d 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -258,6 +258,16 @@ config DRM_GPUVM
          GPU-VM representation providing helpers to manage a GPUs virtual
          address space
 
+config DRM_TTM_BACKUP_FAULT_INJECT
+       bool "Enable fault injection during TTM backup"
+       depends on DRM_TTM
+       default n
+       help
+         Inject recoverable failures during TTM backup and recovery of
+         backed-up 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 38e50cf81b0a..d32a1f2e5e50 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -431,6 +431,7 @@ static int ttm_pool_restore_tt(struct ttm_pool_tt_restore 
*restore,
                               struct ttm_backup *backup,
                               struct ttm_operation_ctx *ctx)
 {
+       static unsigned long __maybe_unused swappedin;
        unsigned int i, nr = 1 << restore->order;
        int ret = 0;
 
@@ -446,6 +447,13 @@ static int ttm_pool_restore_tt(struct ttm_pool_tt_restore 
*restore,
                        if (handle == 0)
                                continue;
 
+                       if (IS_ENABLED(CONFIG_DRM_TTM_BACKUP_FAULT_INJECT) &&
+                           ctx->interruptible &&
+                           ++swappedin % 100 == 0) {
+                               ret = -EINTR;
+                               break;
+                       }
+
                        ret = backup->ops->copy_backed_up_page
                                (backup, restore->first_page[i],
                                 handle, ctx->interruptible);
@@ -892,7 +900,14 @@ long ttm_pool_backup_tt(struct ttm_pool *pool, struct 
ttm_tt *ttm, bool purge,
 
        alloc_gfp = GFP_KERNEL | __GFP_HIGH | __GFP_NOWARN | 
__GFP_RETRY_MAYFAIL;
 
-       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_BACKUP_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;
-- 
2.44.0