Messages in this thread | | | Subject | Re: [PATCH 2/2] [media] vb2: Fix error handling in '__vb2_buf_mem_alloc' | From | Christophe JAILLET <> | Date | Mon, 24 Apr 2017 22:25:18 +0200 |
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Le 24/04/2017 à 16:23, Sakari Ailus a écrit : > Hi Christophe, > > On Sun, Apr 23, 2017 at 11:40:30PM +0200, Christophe JAILLET wrote: >> 'call_ptr_memop' can return NULL, so we must test its return value with >> 'IS_ERR_OR_NULL'. Otherwise, the test 'if (mem_priv)' is meaningless. >> >> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> >> --- >> Note that error checking after 'call_ptr_memop' calls is not consistent >> in this file. I guess that 'IS_ERR_OR_NULL' should be used everywhere >> and that the corresponding error handling code should be tweaked just as >> the code in this function. >> --- >> drivers/media/v4l2-core/videobuf2-core.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c >> index c0175ea7e7ad..d1d3f5dd57b9 100644 >> --- a/drivers/media/v4l2-core/videobuf2-core.c >> +++ b/drivers/media/v4l2-core/videobuf2-core.c >> @@ -210,7 +210,7 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb) >> mem_priv = call_ptr_memop(vb, alloc, >> q->alloc_devs[plane] ? : q->dev, >> q->dma_attrs, size, dma_dir, q->gfp_flags); >> - if (IS_ERR(mem_priv)) { >> + if (IS_ERR_OR_NULL(mem_priv)) { >> if (mem_priv) >> ret = PTR_ERR(mem_priv); >> goto free; > If NULL will always equate -ENOMEM, shouldn't call_ptr_memop() be changed > instead to convert NULL to ERR_PTR(-ENOMEM)? > I agree with you, but in fact, I don't know if "NULL will always equate -ENOMEM"
The return value of 'call_ptr_memop' is likely the result of a function called via a function pointer. I don't know if this function can return NULL or not. I don't know the code enough to see if it would be safe and if this assertion is correct.
So the easiest for me is to just propose a fix to accept NULL.
*** Digging deeper ***
In 'videobuf2-core.h', there is:
/** * struct vb2_mem_ops - memory handling/memory allocator operations * @alloc: allocate video memory and, optionally, allocator private data, * return ERR_PTR() on failure or a pointer to allocator private, * per-buffer data on success; the returned private structure * will then be passed as @buf_priv argument to other ops in this * structure. Additional gfp_flags to use when allocating the * are also passed to this operation. These flags are from the * gfp_flags field of vb2_queue.
So the 'alloc' function should return an ERR_PTR in case of error. 'vb2_vmalloc_alloc', 'vb2_dc_alloc' and 'vb2_dma_sg_alloc' does. (confirmed by code inspection, based on the 'standard' list of alloc functions found in see https://lwn.net/Articles/447435/)
But what if a module implements its own set of functions and returns NULL in such a case?
Anyway, I will propose a patch that returns ERR_PTR(-ENOMEM) instead of NULL, but I won't be able to test it on my own.
Thanks,
CJ
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