Re: [PATCH] staging: comedi: add error handling for vmap

[Ian Abbott]

On 14/06/18 08:57, Zhouyang Jia wrote:
> Hi,
>
> I reported this bug since more than 90% callsites of vmap are
> well handled in kernel. The caller functionÂ__comedi_buf_alloc
> has no return value, so I don't know how the error is handled in
> its caller.
>
> I believe there would be a better error handling method, but I
> have limited domain knowledge, so I'm sorry I can't help here.
>
> Thanks for your kind reply.
>
> Best,
> Zhouyang

__comedi_buf_alloc is just a helper function factored out of, and called 
by comedi_buf_alloc.  __comedi_buf_alloc does not clean up after itself 
on error because it expects comedi_buf_alloc to detect the error and 
call __comedi_buf_free to clean up any partially allocated mess:

    __comedi_buf_alloc(dev, s, n_pages);
    if (!async->prealloc_buf) {
        /*
         * [This is not the actual comment in the code!]
         *
         * Error occured in __comedi_buf_alloc().
         * Buffer may be partially allocated.
         * Call __comedi_buf_free() to clean it up.
         */
        __comedi_buf_free(dev, s);
        return -ENOMEM;
    }

> 2018-06-12 19:50 GMT+08:00 Dan Carpenter <dan.carpenter@xxxxxxxxxx 
> <mailto:dan.carpenter@xxxxxxxxxx>>:
>
>     On Tue, Jun 12, 2018 at 11:25:35AM +0800, Zhouyang Jia wrote:
>     > When vmap fails, the lack of error-handling code may
>     > cause unexpected results.
>     > 
>     > This patch adds error-handling code after calling vmap.
>     > 
>
>     Again, this is not error handling, this is just an error message. This
>     error condition is handled in the caller.
>
>     regards,
>     dan carpenter


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