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SubjectRe: [linux-next PATCH] rapidio: Fix error handling path
On Wed, Sep 16, 2020 at 09:12:17AM +0530, Souptick Joarder wrote:
> There is an error when pin_user_pages_fast() returns -ERRNO and
> inside error handling path driver end up calling unpin_user_pages()
> with -ERRNO which is not correct.
>
> This patch will fix the problem.

There are a few ways we could prevent bug in the future.

1) This could have been caught with existing static analysis tools
which warn about when a value is set but not used.

2) I've created a Smatch check which warngs about:

drivers/rapidio/devices/rio_mport_cdev.c:955 rio_dma_transfer() warn: unpinning negative pages 'nr_pages'

I'll test it out tonight and see how well it works. I don't
immediately see any other bugs allthough Smatch doesn't like the code
in siw_umem_release(). It uses "min_t(int" which suggests that
negative pages are okay.

int to_free = min_t(int, PAGES_PER_CHUNK, num_pages);

3) We could add a check in unpin_user_pages().

if (WARN_ON(IS_ERR_VALUE(npages)))
return;

It's not possible to pin more than "ULONG_MAX - 4095" because otherwise
returning error pointers wouldn't work. So this check can't break
anything and it could prevent a crash.

regards,
dan carpenter

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