Re: [PATCH v2] RDMA/umem: minor bug fix and cleanup in error handling paths

[John Hubbard]

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@xxxxxxxxx wrote:
> > > From: John Hubbard <jhubbard@xxxxxxxxxx>
> > >
> > > ...
> > > 3. Dead code removal: the check for (user_virt & ~page_mask)
> > > is checking for a condition that can never happen,
> > > because earlier:
> > >
> > > ÂÂÂÂ user_virt = user_virt & page_mask;
> > >
> > > ...so, remove that entire phrase.
> > >
> > > ÂÂÂÂÂÂÂÂÂ bcnt -= min_t(size_t, npages << PAGE_SHIFT, bcnt);
> > > ÂÂÂÂÂÂÂÂÂ mutex_lock(&umem_odp->umem_mutex);
> > > ÂÂÂÂÂÂÂÂÂ for (j = 0; j < npages; j++, user_virt += PAGE_SIZE) {
> > > -ÂÂÂÂÂÂÂÂÂÂÂ if (user_virt & ~page_mask) {
> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ p += PAGE_SIZE;
> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (page_to_phys(local_page_list[j]) != p) {
> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ret = -EFAULT;
> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ break;
> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ }
> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ put_page(local_page_list[j]);
> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ continue;
> > > -ÂÂÂÂÂÂÂÂÂÂÂ }
> > > -
> >
> > 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:

@@ -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