Messages in this thread | | | Subject | Re: [linux-next PATCH] rapidio: Fix error handling path | From | John Hubbard <> | Date | Thu, 17 Sep 2020 10:47:26 -0700 |
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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.
> > 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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