[linux-next:master 8015/8469] drivers/gpu/drm/i915/i915_mm.c:76 remap_io_sg() error: uninitialized symbol 'err'.

[linux-next:master 8015/8469] drivers/gpu/drm/i915/i915_mm.c:76 remap_io_sg() error: uninitialized symbol 'err'.

[Dan Carpenter]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   9d49ed9ca93b8c564033c1d6808017bc9052b5db
commit: 204302d90503407d2af233c1222b2e79f35580f3 [8015/8469] i915: fix remap_io_sg to verify the pgprot
config: i386-randconfig-m021-20210329 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>

smatch warnings:
drivers/gpu/drm/i915/i915_mm.c:76 remap_io_sg() error: uninitialized symbol 'err'.

vim +/err +76 drivers/gpu/drm/i915/i915_mm.c

4e598fad226be0 Abdiel Janulgue   2020-01-03  45  int remap_io_sg(struct vm_area_struct *vma,
1764b992be0f1c Abdiel Janulgue   2019-12-31  46  		unsigned long addr, unsigned long size,
4e598fad226be0 Abdiel Janulgue   2020-01-03  47  		struct scatterlist *sgl, resource_size_t iobase)
1764b992be0f1c Abdiel Janulgue   2019-12-31  48  {
204302d9050340 Christoph Hellwig 2021-03-29  49  	unsigned long pfn, len, remapped = 0;
1764b992be0f1c Abdiel Janulgue   2019-12-31  50  	int err;
1764b992be0f1c Abdiel Janulgue   2019-12-31  51  
1764b992be0f1c Abdiel Janulgue   2019-12-31  52  	/* We rely on prevalidation of the io-mapping to skip track_pfn(). */
1764b992be0f1c Abdiel Janulgue   2019-12-31  53  	GEM_BUG_ON((vma->vm_flags & EXPECTED_FLAGS) != EXPECTED_FLAGS);
1764b992be0f1c Abdiel Janulgue   2019-12-31  54  
4e598fad226be0 Abdiel Janulgue   2020-01-03  55  	if (!use_dma(iobase))
1764b992be0f1c Abdiel Janulgue   2019-12-31  56  		flush_cache_range(vma, addr, size);
4e598fad226be0 Abdiel Janulgue   2020-01-03  57  
204302d9050340 Christoph Hellwig 2021-03-29  58  	do {
204302d9050340 Christoph Hellwig 2021-03-29  59  		if (use_dma(iobase)) {
204302d9050340 Christoph Hellwig 2021-03-29  60  			if (!sg_dma_len(sgl))
204302d9050340 Christoph Hellwig 2021-03-29  61  				break;
                                                                                ^^^^^
Can this break on the first iteration through the loop?

204302d9050340 Christoph Hellwig 2021-03-29  62  			pfn = (sg_dma_address(sgl) + iobase) >> PAGE_SHIFT;
204302d9050340 Christoph Hellwig 2021-03-29  63  			len = sg_dma_len(sgl);
204302d9050340 Christoph Hellwig 2021-03-29  64  		} else {
204302d9050340 Christoph Hellwig 2021-03-29  65  			pfn = page_to_pfn(sg_page(sgl));
204302d9050340 Christoph Hellwig 2021-03-29  66  			len = sgl->length;
1764b992be0f1c Abdiel Janulgue   2019-12-31  67  		}
1764b992be0f1c Abdiel Janulgue   2019-12-31  68  
204302d9050340 Christoph Hellwig 2021-03-29  69  		err = remap_pfn_range(vma, addr + remapped, pfn, len,
204302d9050340 Christoph Hellwig 2021-03-29  70  				      vma->vm_page_prot);
204302d9050340 Christoph Hellwig 2021-03-29  71  		if (err)
204302d9050340 Christoph Hellwig 2021-03-29  72  			break;
204302d9050340 Christoph Hellwig 2021-03-29  73  		remapped += len;
204302d9050340 Christoph Hellwig 2021-03-29  74  	} while ((sgl = __sg_next(sgl)));
204302d9050340 Christoph Hellwig 2021-03-29  75  
204302d9050340 Christoph Hellwig 2021-03-29 @76  	if (err)

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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Re: [linux-next:master 8015/8469] drivers/gpu/drm/i915/i915_mm.c:76 remap_io_sg() error: uninitialized symbol 'err'.

[Christoph Hellwig]

On Tue, Mar 30, 2021 at 01:01:52PM +0300, Dan Carpenter wrote:
> drivers/gpu/drm/i915/i915_mm.c:76 remap_io_sg() error: uninitialized symbol 'err'.

Having an SGL where the first entry has a 0 dma_length is not valid.
That being said, the trivial patch below will remove the warning and
is otherwise harmless, so we could fold it in:

diff --git a/drivers/gpu/drm/i915/i915_mm.c b/drivers/gpu/drm/i915/i915_mm.c
index 4c8cd08c672d2d..25576fa73ff031 100644
--- a/drivers/gpu/drm/i915/i915_mm.c
+++ b/drivers/gpu/drm/i915/i915_mm.c
@@ -47,7 +47,7 @@ int remap_io_sg(struct vm_area_struct *vma,
 		struct scatterlist *sgl, resource_size_t iobase)
 {
 	unsigned long pfn, len, remapped = 0;
-	int err;
+	int err = 0;
 
 	/* We rely on prevalidation of the io-mapping to skip track_pfn(). */
 	GEM_BUG_ON((vma->vm_flags & EXPECTED_FLAGS) != EXPECTED_FLAGS);