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    SubjectRe: [PATCH v2] RDMA/umem: minor bug fix and cleanup in error handling paths
    On Sun, Mar 03, 2019 at 02:37:33PM -0800, John Hubbard wrote:
    > On 3/3/19 1:52 AM, Artemy Kovalyov wrote:
    > >
    > >
    > > On 02/03/2019 21:44, Ira Weiny wrote:
    > > >
    > > > On Sat, Mar 02, 2019 at 12:24:35PM -0800, john.hubbard@gmail.com wrote:
    > > > > From: John Hubbard <jhubbard@nvidia.com>
    > > > >
    > > > > ...
    > > > > 3. Dead code removal: the check for (user_virt & ~page_mask)
    > > > > is checking for a condition that can never happen,
    > > > > because earlier:
    > > > >
    > > > >      user_virt = user_virt & page_mask;
    > > > >
    > > > > ...so, remove that entire phrase.
    > > > >
    > > > >           bcnt -= min_t(size_t, npages << PAGE_SHIFT, bcnt);
    > > > >           mutex_lock(&umem_odp->umem_mutex);
    > > > >           for (j = 0; j < npages; j++, user_virt += PAGE_SIZE) {
    > > > > -            if (user_virt & ~page_mask) {
    > > > > -                p += PAGE_SIZE;
    > > > > -                if (page_to_phys(local_page_list[j]) != p) {
    > > > > -                    ret = -EFAULT;
    > > > > -                    break;
    > > > > -                }
    > > > > -                put_page(local_page_list[j]);
    > > > > -                continue;
    > > > > -            }
    > > > > -
    > > >
    > > > I think this is trying to account for compound pages. (ie page_mask could
    > > > represent more than PAGE_SIZE which is what user_virt is being incrimented by.)
    > > > But putting the page in that case seems to be the wrong thing to do?
    > > >
    > > > Yes this was added by Artemy[1] now cc'ed.
    > >
    > > Right, this is for huge pages, please keep it.
    > > put_page() needed to decrement refcount of the head page.
    > >
    >
    > OK, thanks for explaining! Artemy, while you're here, any thoughts about the
    > release_pages, and the change of the starting point, from the other part
    > of the patch:

    Your release pages code is right fix, it will be great if you prepare
    proper and standalone patch.

    Thanks

    >
    > @@ -684,9 +677,11 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp
    > *umem_odp, u64 user_virt,
    > mutex_unlock(&umem_odp->umem_mutex);
    >
    > if (ret < 0) {
    > - /* Release left over pages when handling errors. */
    > - for (++j; j < npages; ++j)
    > - put_page(local_page_list[j]);
    > + /*
    > + * Release pages, starting at the the first page
    > + * that experienced an error.
    > + */
    > + release_pages(&local_page_list[j], npages - j);
    > break;
    > }
    > }
    >
    > ?
    >
    > thanks,
    > --
    > John Hubbard
    > NVIDIA
    >
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