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SubjectRe: [PATCH 3/3] drm/i915/selftests: avoid bogus maybe-uninitialized warning
Date
Quoting Arnd Bergmann (2020-05-27 15:05:10)
> gcc has a problem following values through IS_ERR/PTR_ERR macros,
> leading to a false-positive warning in allmodconfig, with any
> compiler version:
>
> In file included from drivers/gpu/drm/i915/gt/intel_lrc.c:5892:
> drivers/gpu/drm/i915/gt/selftest_lrc.c: In function 'create_gpr_client.isra.0':
> drivers/gpu/drm/i915/gt/selftest_lrc.c:2902:23: error: 'rq' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> This one is hard to avoid without impairing readability or adding a
> bugus NULL pointer.
>
> Fixes: c92724de6db1 ("drm/i915/selftests: Try to detect rollback during batchbuffer preemption")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/gpu/drm/i915/gt/selftest_lrc.c | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> index 824f99c4cc7c..933c3f5adf0a 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> @@ -2908,23 +2908,25 @@ create_gpr_client(struct intel_engine_cs *engine,
>
> vma = i915_vma_instance(global->obj, ce->vm, NULL);
> if (IS_ERR(vma)) {
> - err = PTR_ERR(vma);
> + rq = ERR_CAST(vma);
> goto out_ce;
> }
>
> err = i915_vma_pin(vma, 0, 0, PIN_USER);
> - if (err)
> + if (err) {
> + rq = ERR_PTR(err);
> goto out_ce;
> + }
>
> batch = create_gpr_user(engine, vma, offset);
> if (IS_ERR(batch)) {
> - err = PTR_ERR(batch);
> + rq = ERR_CAST(batch);
> goto out_vma;
> }
>
> rq = intel_context_create_request(ce);
> if (IS_ERR(rq)) {
> - err = PTR_ERR(rq);
> + rq = ERR_CAST(rq);
> goto out_batch;
> }
>
> @@ -2946,17 +2948,20 @@ create_gpr_client(struct intel_engine_cs *engine,
> i915_vma_unlock(batch);
> i915_vma_unpin(batch);
>
> - if (!err)
> + if (!err) {
> i915_request_get(rq);
> - i915_request_add(rq);
> -
> + i915_request_add(rq);
> + } else {
> + i915_request_add(rq);
> + rq = ERR_PTR(err);
> + }
> out_batch:
> i915_vma_put(batch);
> out_vma:
> i915_vma_unpin(vma);
> out_ce:
> intel_context_put(ce);
> - return err ? ERR_PTR(err) : rq;
> + return rq;

Hmm, I've used this style a few times, so could do with some syntactic
refinement.

drivers/gpu/drm/i915/gem/i915_gem_userptr.c: return err ? ERR_PTR(err) : mm->mn;
drivers/gpu/drm/i915/gt/selftest_hangcheck.c: return err ? ERR_PTR(err) : rq;
drivers/gpu/drm/i915/gt/selftest_lrc.c: return err ? ERR_PTR(err) : rq;
drivers/gpu/drm/i915/selftests/i915_gem_gtt.c: return err ? ERR_PTR(err) : rq;
drivers/gpu/drm/i915/selftests/i915_request.c: return err ? ERR_PTR(err) : request;
drivers/gpu/drm/i915/selftests/igt_spinner.c: return err ? ERR_PTR(err) : rq;
-Chris

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