linux-kernel - Re: drivers/gpu/drm/vc4/vc4_gem.c:604 vc4_lock_bo_reservations() error: uninitialized symbol 'ret'.

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Message-ID: <b402252a-91de-4983-abc1-65f78e7e6ae7@igalia.com>
Date: Wed, 9 Apr 2025 16:49:45 -0300
From: Maíra Canal <mcanal@...lia.com>
To: Dan Carpenter <dan.carpenter@...aro.org>, oe-kbuild@...ts.linux.dev,
 Christian König <christian.koenig@....com>
Cc: lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
 linux-kernel@...r.kernel.org, Melissa Wen <mwen@...lia.com>
Subject: Re: drivers/gpu/drm/vc4/vc4_gem.c:604 vc4_lock_bo_reservations()
 error: uninitialized symbol 'ret'.

+ König

Hi Dan,

On 02/04/25 05:43, Dan Carpenter wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   acc4d5ff0b61eb1715c498b6536c38c1feb7f3c1
> commit: 04630796c437a9285643097825cbd3cd06603f47 drm/vc4: Use DRM Execution Contexts
> date:   2 months ago
> config: arm64-randconfig-r073-20250402 (https://download.01.org/0day-ci/archive/20250402/202504021500.3AM1hKKS-lkp@intel.com/config)
> compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> | Closes: https://lore.kernel.org/r/202504021500.3AM1hKKS-lkp@intel.com/
> 
> smatch warnings:
> drivers/gpu/drm/vc4/vc4_gem.c:604 vc4_lock_bo_reservations() error: uninitialized symbol 'ret'.
> 
> vim +/ret +604 drivers/gpu/drm/vc4/vc4_gem.c
> 
> cdec4d3613230f Eric Anholt 2017-04-12  589  static int
> 04630796c437a9 Maíra Canal 2024-12-20  590  vc4_lock_bo_reservations(struct vc4_exec_info *exec,
> 04630796c437a9 Maíra Canal 2024-12-20  591  			 struct drm_exec *exec_ctx)
> cdec4d3613230f Eric Anholt 2017-04-12  592  {
> 04630796c437a9 Maíra Canal 2024-12-20  593  	int ret;
> cdec4d3613230f Eric Anholt 2017-04-12  594
> cdec4d3613230f Eric Anholt 2017-04-12  595  	/* Reserve space for our shared (read-only) fence references,
> cdec4d3613230f Eric Anholt 2017-04-12  596  	 * before we commit the CL to the hardware.
> cdec4d3613230f Eric Anholt 2017-04-12  597  	 */
> 04630796c437a9 Maíra Canal 2024-12-20  598  	drm_exec_init(exec_ctx, DRM_EXEC_INTERRUPTIBLE_WAIT, exec->bo_count);
> 04630796c437a9 Maíra Canal 2024-12-20  599  	drm_exec_until_all_locked(exec_ctx) {
> 04630796c437a9 Maíra Canal 2024-12-20  600  		ret = drm_exec_prepare_array(exec_ctx, exec->bo,
> 04630796c437a9 Maíra Canal 2024-12-20  601  					     exec->bo_count, 1);
> 
> This is a false positive in Smatch.  I can silence the warning on my
> end easily enough to say that we always enter the drm_exec_until_all_locked()
> loop.  But the question is why do we only test the last "ret" instead of
> testing all of them?

AFAIU `drm_exec_until_all_locked` will loop until all GEM objects are
locked and no more contention exists. As we have a single operation
inside the loop, we don't need to check "ret" for every iteration.

I believe Christian will possibly give you a more precise answer as he
designed the API.

Best Regards,
- Maíra

> 
> 04630796c437a9 Maíra Canal 2024-12-20  602  	}
> cdec4d3613230f Eric Anholt 2017-04-12  603
> cdec4d3613230f Eric Anholt 2017-04-12 @604  	if (ret) {
> 04630796c437a9 Maíra Canal 2024-12-20  605  		drm_exec_fini(exec_ctx);
> cdec4d3613230f Eric Anholt 2017-04-12  606  		return ret;
> 7edabee06a5622 Eric Anholt 2016-09-27  607  	}
> d5b1a78a772f1e Eric Anholt 2015-11-30  608
> cdec4d3613230f Eric Anholt 2017-04-12  609  	return 0;
> cdec4d3613230f Eric Anholt 2017-04-12  610  }
>