2018-06-12 03:27:44

by Zhouyang Jia

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

When vmap fails, the lack of error-handling code may
cause unexpected results.

This patch adds error-handling code after calling vmap.

Signed-off-by: Zhouyang Jia <[email protected]>
---
drivers/staging/comedi/comedi_buf.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/comedi_buf.c b/drivers/staging/comedi/comedi_buf.c
index f693c2c..5e48693 100644
--- a/drivers/staging/comedi/comedi_buf.c
+++ b/drivers/staging/comedi/comedi_buf.c
@@ -132,9 +132,12 @@ static void __comedi_buf_alloc(struct comedi_device *dev,
spin_unlock_irqrestore(&s->spin_lock, flags);

/* vmap the prealloc_buf if all the pages were allocated */
- if (i == n_pages)
+ if (i == n_pages) {
async->prealloc_buf = vmap(pages, n_pages, VM_MAP,
COMEDI_PAGE_PROTECTION);
+ if (!async->prealloc_buf)
+ dev_err(dev->class_dev, "failed to vmap pages\n");
+ }

vfree(pages);
}
--
2.7.4

2018-06-12 11:52:09

by Dan Carpenter

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

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

2018-06-14 10:00:44

by Ian Abbott

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

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 function __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 <[email protected]
> <mailto:[email protected]>>:
>
> 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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