On Wed, Jul 18, 2018 at 11:14:04AM +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.
As the first version made it into -stable unfortunately I would ask
for a review on this V3 so that a correct fix could go into -stabele
ASAP.
thx!
hofrat
>
> Signed-off-by: Nicholas Mc Guire <hof...@osadl.org>
> Reported-by: kbuild test robot <l...@intel.com>
> Reported-by: Sean Paul <seanp...@chromium.org>
> Fixes: d530b5f1ca0b ("drm: re-enable error handling")
> Fixes: 62968144e673 ("drm: convert drm context code to use Linux idr")
> ---
>
> V3: bug in patch - omission to remove old code properly - V3 fixes the
> original problem as proposed in V2 and drops the excess line.
> reported by Sean Paul <seanp...@chromium.org> - thanks!
>
> 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 <l...@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-rc5 (localversion-next is next-20180718)
>
> drivers/gpu/drm/drm_context.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_context.c b/drivers/gpu/drm/drm_context.c
> index f973d28..ad268c8 100644
> --- a/drivers/gpu/drm/drm_context.c
> +++ b/drivers/gpu/drm/drm_context.c
> @@ -361,22 +361,25 @@ 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);
> - 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
>
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