Messages in this thread | | | Date | Fri, 31 Oct 2014 12:06:58 -0700 | From | Peter Feiner <> | Subject | Re: [PATCH 4/5] mm: gup: use get_user_pages_unlocked |
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On Wed, Oct 29, 2014 at 05:35:19PM +0100, Andrea Arcangeli wrote: > This allows those get_user_pages calls to pass FAULT_FLAG_ALLOW_RETRY > to the page fault in order to release the mmap_sem during the I/O. > > Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Peter Feiner <pfeiner@google.com>
> diff --git a/net/ceph/pagevec.c b/net/ceph/pagevec.c > index 5550130..096d914 100644 > --- a/net/ceph/pagevec.c > +++ b/net/ceph/pagevec.c > @@ -23,17 +23,15 @@ struct page **ceph_get_direct_page_vector(const void __user *data, > if (!pages) > return ERR_PTR(-ENOMEM); > > - down_read(¤t->mm->mmap_sem); > while (got < num_pages) { > - rc = get_user_pages(current, current->mm, > + rc = get_user_pages_unlocked(current, current->mm, > (unsigned long)data + ((unsigned long)got * PAGE_SIZE), > - num_pages - got, write_page, 0, pages + got, NULL); > + num_pages - got, write_page, 0, pages + got); > if (rc < 0) > break; > BUG_ON(rc == 0); > got += rc; > } > - up_read(¤t->mm->mmap_sem); > if (rc < 0) > goto fail; > return pages;
I spent a while looking at this to make sure that BUG_ON(rc == 0) won't trigger. AFAICT, __get_user_pages_locked can't return 0 since __get_user_pages only returns 0 when nonblocking is not NULL; when __get_user_pages_locked calls __get_user_pages with nonblocking != NULL (i.e., the first call in the body of the for(;;) loop) and __get_user_pages returns 0, then __get_user_pages_locked will call __get_user_pages again with nonblocking == NULL.
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