Messages in this thread | | | From | Souptick Joarder <> | Date | Fri, 18 Sep 2020 07:51:59 +0530 | Subject | Re: [linux-next PATCH] rapidio: Fix error handling path |
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On Thu, Sep 17, 2020 at 11:17 PM John Hubbard <jhubbard@nvidia.com> wrote: > > On 9/17/20 10:34 AM, Ira Weiny wrote: > > On Thu, Sep 17, 2020 at 03:39:51PM +0300, Dan Carpenter wrote: > >> On Wed, Sep 16, 2020 at 01:02:32PM +0300, Dan Carpenter wrote: > >>> 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); > >>> > >> > >> I only found one bug but I'm going to add unpin_user_pages_dirty_lock() > >> to the mix a retest. There were a few other false positives. In > >> reviewing the code, I noticed that orangefs_bufmap_map() is also buggy. > >> > >> I sort of feel like returning partial successes is not working. We > >> could easily make a wrapper which either pins everything or it returns > >> an error code. > > Yes we could. And I have the same feeling about this API. It's generated a > remarkable amount of bug fixes, several of which ended up being partial or > wrong in themselves. And mostly this is due to the complicated tristate > return code: instead of 0 or -ERRNO, it also can return "N pages that is > less than what you requested", and there are no standard helpers in the kernel > to make that easier to deal with
There was some discussion on removing return value 0 from one of the gup variants [1]. I think it might be partially relevant to the current discussion.
[1] https://patchwork.kernel.org/patch/11529795/
> > > > > I guess the question is are there drivers which will keep working (or limp > > along?) on partial pins? A quick search of a driver I thought did this does > > not apparently any more... So it sounds good to me from 30,000 feet! :-D > > It sounds good to me too--and from just a *few hundred feet* (having touched most > of the call sites at some point)! haha :) > > I think the wrapper should be short-term, though, just until all the callers > are converted to the simpler API. Then change the core gup/pup calls to the simpler > API. There are more than enough gup/pup API entry points as it is, that's for sure. > > > thanks, > -- > John Hubbard > NVIDIA
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