On Tue, Jul 17, 2018 at 04:14:16PM -0400, Sean Paul wrote:

On Tue, Jul 17, 2018 at 03:28:21PM +0200, Nicholas Mc Guire wrote:

...

drm_legacy_ctxbitmap_next() returns idr_alloc() which can return -ENOMEM, -EINVAL or -ENOSPC none of which are -1. since drm_context_t is an unsigned int an intermediate variable is used to handle the error cases, and then cast to drm_context_t after ensuring that the value is >= 0. The explicit cast is to mark the type conversion as intentional.

Signed-off-by: Nicholas Mc Guire hofrat@osadl.org Reported-by: kbuild test robot lkp@intel.com Fixes: d530b5f1ca0b ("drm: re-enable error handling") Fixes: 62968144e673 ("drm: convert drm context code to use Linux idr")

---

kbuild test robot reported:

<snip> tree: git://anongit.freedesktop.org/drm/drm-misc for-linux-next-fixes head: d530b5f1ca0bb66958a2b714bebe40a1248b9c15 commit: d530b5f1ca0bb66958a2b714bebe40a1248b9c15 [2/2] drm: re-enable error +handling

smatch warnings: drivers/gpu/drm/drm_context.c:375 drm_legacy_addctx() warn: unsigned +'ctx->handle' is never less than zero.

<snip>

V2: The proposed fix in d530b5f1ca0b ("drm: re-enable error handling") actually was ineffective as the negative return value check was against a unsigned int and thus always false as reported by kbuild test robot lkp@intel.com. The below patch removes that warning and fixes the original problem of missed error handling.

drm_context_t is actually just used in a few placed so the type could be changed but it is also exported via tools/include/uapi/drm/drm.h so changing the typedef of drm_context_t could break applications and thus this is not an option.

Patch was compile tested with: x86_64_defconfig

Patch is against 4.18-rc4 (localversion-next is next-20180717)

drivers/gpu/drm/drm_context.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_context.c b/drivers/gpu/drm/drm_context.c index 3c4000f..78f32a3 100644 --- a/drivers/gpu/drm/drm_context.c +++ b/drivers/gpu/drm/drm_context.c @@ -361,22 +361,26 @@ int drm_legacy_addctx(struct drm_device *dev, void *data, { struct drm_ctx_list *ctx_entry; struct drm_ctx *ctx = data;

• int ret;

  if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) && !drm_core_check_feature(dev, DRIVER_LEGACY)) return -EINVAL;

  ctx->handle = drm_legacy_ctxbitmap_next(dev);

Remove this call?

yup - forgot to remove that line after copying

The modified block should be: int ret; ...

ret = drm_legacy_ctxbitmap_next(dev); if (ret == DRM_KERNEL_CONTEXT) { /* Skip kernel's context and get a new one. */ ret = drm_legacy_ctxbitmap_next(dev); } DRM_DEBUG("ctxbitmap is error code %d\n", ret); if (ret < 0) { DRM_DEBUG("Not enough free contexts.\n"); /* Should this return -EBUSY instead? */ return -ENOMEM; } /* valid context is >= 0 */ ctx->handle = (drm_context_t)ret;

thanks for cathcing that - will resend

thx! hofrat

...

• if (ctx->handle == DRM_KERNEL_CONTEXT) {

• ret = drm_legacy_ctxbitmap_next(dev);
• if (ret == DRM_KERNEL_CONTEXT) { /* Skip kernel's context and get a new one. */

• ctx->handle = drm_legacy_ctxbitmap_next(dev);
  

• ret = drm_legacy_ctxbitmap_next(dev);
  

  }

• DRM_DEBUG("%d\n", ctx->handle);
• if (ctx->handle < 0) {

• DRM_DEBUG("ctxbitmap is error code %d\n", ret);

• if (ret < 0) { DRM_DEBUG("Not enough free contexts.\n"); /* Should this return -EBUSY instead? */ return -ENOMEM; }

• /* valid context is >= 0 */

• ctx->handle = (drm_context_t)ret;

  ctx_entry = kmalloc(sizeof(*ctx_entry), GFP_KERNEL); if (!ctx_entry) {

-- 2.1.4

-- Sean Paul, Software Engineer, Google / Chromium OS