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

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Message-ID: <20190304064419.GB15253@mtr-leonro.mtl.com>
Date:   Mon, 4 Mar 2019 08:44:19 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Artemy Kovalyov <artemyko@...lanox.com>,
        Ira Weiny <ira.weiny@...el.com>,
        "john.hubbard@...il.com" <john.hubbard@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Doug Ledford <dledford@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: Re: [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@...il.com wrote:
> > > > From: John Hubbard <jhubbard@...dia.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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