Re: [PATCH] Use of getblk differs between locations

From: Glauber de Oliveira Costa
Date: Mon Oct 10 2005 - 16:36:31 EST

On Mon, Oct 10, 2005 at 10:20:07PM +0100, Anton Altaparmakov wrote:
> Hi,
> On Mon, 10 Oct 2005, Glauber de Oliveira Costa wrote:
> > I've just noticed that the use of sb_getblk differs between locations
> > inside the kernel. To be precise, in some locations there are tests
> > against its return value, and in some places there are not.
> >
> > According to the comments in __getblk definition, the tests are not
> > necessary, as the function always return a buffer_head (maybe a wrong
> > one),
> If you had read the source code rather than just the comments you would
> have seen that this is not true. It can return NULL (see
> fs/buffer.c::__getblk_slow()). Certainly I would prefer to keep the
> checks in NTFS, please. They may only be good for catching bugs but I
> like catching bugs rather than segfaulting due to a NULL dereference.

I did. But I did not see this specifically, for sure. What takes us to
the opposite problem: A lot of places do not check for the return value
of getblk (Almost half of them, I'd say), and may thus lead to a
dereferencing of a NULL pointer.

Does anyone else have any comments on that?

> Best regards,
> Anton

> --
> Anton Altaparmakov <aia21 at> (replace at with @)
> Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
> Linux NTFS maintainer / IRC: #ntfs on
> WWW: &

Glauber de Oliveira Costa
IBM Linux Technology Center - Brazil
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