From: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
To: Luis Henriques <lhenriques@suse.de>
Cc: Amir Goldstein <amir73il@gmail.com>,
Trond Myklebust <trondmy@hammerspace.com>,
"samba-technical@lists.samba.org"
<samba-technical@lists.samba.org>,
"drinkcat@chromium.org" <drinkcat@chromium.org>,
"iant@google.com" <iant@google.com>,
"linux-cifs@vger.kernel.org" <linux-cifs@vger.kernel.org>,
"darrick.wong@oracle.com" <darrick.wong@oracle.com>,
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"jlayton@kernel.org" <jlayton@kernel.org>,
"anna.schumaker@netapp.com" <anna.schumaker@netapp.com>,
"llozano@chromium.org" <llozano@chromium.org>,
"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
"miklos@szeredi.hu" <miklos@szeredi.hu>,
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"dchinner@redhat.com" <dchinner@redhat.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"sfrench@samba.org" <sfrench@samba.org>,
"ceph-devel@vger.kernel.org" <ceph-devel@vger.kernel.org>
Subject: Re: [PATCH v2] vfs: prevent copy_file_range to copy across devices
Date: Tue, 16 Feb 2021 12:28:57 +0100 [thread overview]
Message-ID: <YCuseTMyjL+9sWum@kroah.com> (raw)
In-Reply-To: <87r1lgjm7l.fsf@suse.de>
On Tue, Feb 16, 2021 at 11:17:34AM +0000, Luis Henriques wrote:
> Amir Goldstein <amir73il@gmail.com> writes:
>
> > On Mon, Feb 15, 2021 at 8:57 PM Trond Myklebust <trondmy@hammerspace.com> wrote:
> >>
> >> On Mon, 2021-02-15 at 19:24 +0200, Amir Goldstein wrote:
> >> > On Mon, Feb 15, 2021 at 6:53 PM Trond Myklebust <
> >> > trondmy@hammerspace.com> wrote:
> >> > >
> >> > > On Mon, 2021-02-15 at 18:34 +0200, Amir Goldstein wrote:
> >> > > > On Mon, Feb 15, 2021 at 5:42 PM Luis Henriques <
> >> > > > lhenriques@suse.de>
> >> > > > wrote:
> >> > > > >
> >> > > > > Nicolas Boichat reported an issue when trying to use the
> >> > > > > copy_file_range
> >> > > > > syscall on a tracefs file. It failed silently because the file
> >> > > > > content is
> >> > > > > generated on-the-fly (reporting a size of zero) and
> >> > > > > copy_file_range
> >> > > > > needs
> >> > > > > to know in advance how much data is present.
> >> > > > >
> >> > > > > This commit restores the cross-fs restrictions that existed
> >> > > > > prior
> >> > > > > to
> >> > > > > 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
> >> > > > > devices")
> >> > > > > and
> >> > > > > removes generic_copy_file_range() calls from ceph, cifs, fuse,
> >> > > > > and
> >> > > > > nfs.
> >> > > > >
> >> > > > > Fixes: 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
> >> > > > > devices")
> >> > > > > Link:
> >> > > > > https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@chromium.org/
> >> > > > > Cc: Nicolas Boichat <drinkcat@chromium.org>
> >> > > > > Signed-off-by: Luis Henriques <lhenriques@suse.de>
> >> > > >
> >> > > > Code looks ok.
> >> > > > You may add:
> >> > > >
> >> > > > Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> >> > > >
> >> > > > I agree with Trond that the first paragraph of the commit message
> >> > > > could
> >> > > > be improved.
> >> > > > The purpose of this change is to fix the change of behavior that
> >> > > > caused the regression.
> >> > > >
> >> > > > Before v5.3, behavior was -EXDEV and userspace could fallback to
> >> > > > read.
> >> > > > After v5.3, behavior is zero size copy.
> >> > > >
> >> > > > It does not matter so much what makes sense for CFR to do in this
> >> > > > case (generic cross-fs copy). What matters is that nobody asked
> >> > > > for
> >> > > > this change and that it caused problems.
> >> > > >
> >> > >
> >> > > No. I'm saying that this patch should be NACKed unless there is a
> >> > > real
> >> > > explanation for why we give crap about this tracefs corner case and
> >> > > why
> >> > > it can't be fixed.
> >> > >
> >> > > There are plenty of reasons why copy offload across filesystems
> >> > > makes
> >> > > sense, and particularly when you're doing NAS. Clone just doesn't
> >> > > cut
> >> > > it when it comes to disaster recovery (whereas backup to a
> >> > > different
> >> > > storage unit does). If the client has to do the copy, then you're
> >> > > effectively doubling the load on the server, and you're adding
> >> > > potentially unnecessary network traffic (or at the very least you
> >> > > are
> >> > > doubling that traffic).
> >> > >
> >> >
> >> > I don't understand the use case you are describing.
> >> >
> >> > Which filesystem types are you talking about for source and target
> >> > of copy_file_range()?
> >> >
> >> > To be clear, the original change was done to support NFS/CIFS server-
> >> > side
> >> > copy and those should not be affected by this change.
> >> >
> >>
> >> That is incorrect:
> >>
> >> ssize_t nfsd_copy_file_range(struct file *src, u64 src_pos, struct file
> >> *dst,
> >> u64 dst_pos, u64 count)
> >> {
> >>
> >> /*
> >> * Limit copy to 4MB to prevent indefinitely blocking an nfsd
> >> * thread and client rpc slot. The choice of 4MB is somewhat
> >> * arbitrary. We might instead base this on r/wsize, or make it
> >> * tunable, or use a time instead of a byte limit, or implement
> >> * asynchronous copy. In theory a client could also recognize a
> >> * limit like this and pipeline multiple COPY requests.
> >> */
> >> count = min_t(u64, count, 1 << 22);
> >> return vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);
> >> }
> >>
> >> You are now explicitly changing the behaviour of knfsd when the source
> >> and destination filesystem differ.
> >>
> >> For one thing, you are disallowing the NFSv4.2 copy offload use case of
> >> copying from a local filesystem to a remote NFS server. However you are
> >> also disallowing the copy from, say, an XFS formatted partition to an
> >> ext4 partition.
> >>
> >
> > Got it.
>
> Ugh. And I guess overlayfs may have a similar problem.
>
> > This is easy to solve with a flag COPY_FILE_SPLICE (or something) that
> > is internal to kernel users.
> >
> > FWIW, you may want to look at the loop in ovl_copy_up_data()
> > for improvements to nfsd_copy_file_range().
> >
> > We can move the check out to copy_file_range syscall:
> >
> > if (flags != 0)
> > return -EINVAL;
> >
> > Leave the fallback from all filesystems and check for the
> > COPY_FILE_SPLICE flag inside generic_copy_file_range().
>
> Ok, the diff bellow is just to make sure I understood your suggestion.
>
> The patch will also need to:
>
> - change nfs and overlayfs calls to vfs_copy_file_range() so that they
> use the new flag.
>
> - check flags in generic_copy_file_checks() to make sure only valid flags
> are used (COPY_FILE_SPLICE at the moment).
>
> Also, where should this flag be defined? include/uapi/linux/fs.h?
Why would userspace want/need this flag?
next prev parent reply other threads:[~2021-02-16 11:30 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAOQ4uxiFGjdvX2-zh5o46pn7RZhvbGHH0wpzLPuPOom91FwWeQ@mail.gmail.com>
2021-02-15 15:43 ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Luis Henriques
2021-02-15 16:02 ` Trond Myklebust
2021-02-16 0:25 ` Steve French
2021-02-15 16:34 ` Amir Goldstein
2021-02-15 16:53 ` Trond Myklebust
2021-02-15 17:24 ` Amir Goldstein
2021-02-15 18:57 ` Trond Myklebust
2021-02-15 19:43 ` Amir Goldstein
2021-02-16 11:17 ` Luis Henriques
2021-02-16 11:28 ` gregkh [this message]
2021-02-16 12:01 ` Luis Henriques
2021-02-16 12:08 ` Greg KH
2021-02-16 13:51 ` Amir Goldstein
2021-02-16 16:42 ` Luis Henriques
2021-02-16 17:44 ` Amir Goldstein
2021-02-16 18:55 ` Luis Henriques
2021-02-16 19:20 ` Amir Goldstein
2021-02-16 19:27 ` Anna Schumaker
2021-02-16 19:31 ` Steve French
2021-02-16 19:40 ` Amir Goldstein
2021-02-16 21:15 ` Steve French
2021-02-17 8:08 ` Amir Goldstein
2021-02-17 17:26 ` [PATCH v3] vfs: fix copy_file_range regression in cross-fs copies Luis Henriques
2021-02-17 20:47 ` Amir Goldstein
2021-02-18 0:56 ` Nicolas Boichat
2021-02-18 5:32 ` Olga Kornievskaia
2021-02-18 6:47 ` Amir Goldstein
2021-02-18 16:28 ` Olga Kornievskaia
2021-02-18 7:43 ` Christoph Hellwig
2021-02-18 0:50 ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Andreas Dilger
2021-02-18 7:34 ` gregkh
2021-02-16 18:54 ` Andreas Dilger
2021-02-17 4:45 ` Nicolas Boichat
2021-02-18 7:42 ` Christoph Hellwig
2021-02-18 9:10 ` Amir Goldstein
2021-02-18 10:29 ` Luis Henriques
2021-02-18 12:15 ` Luis Henriques
2021-02-18 12:49 ` Amir Goldstein
2021-02-18 14:36 ` [PATCH v4] vfs: fix copy_file_range regression in cross-fs copies Luis Henriques
2021-02-18 14:58 ` Amir Goldstein
2021-02-18 15:17 ` [PATCH v5] " Luis Henriques
2021-02-18 15:53 ` Amir Goldstein
2021-02-18 16:35 ` Luis Henriques
2021-02-18 17:18 ` [PATCH v6] " Luis Henriques
2021-02-19 21:18 ` Olga Kornievskaia
2021-02-19 21:52 ` Amir Goldstein
2021-02-21 19:58 ` [PATCH v7] " Luis Henriques
2021-02-22 3:00 ` Nicolas Boichat
2021-02-22 10:24 ` [PATCH v8] " Luis Henriques
2021-02-22 10:46 ` Amir Goldstein
2021-02-22 16:25 ` dai.ngo
2021-02-23 10:32 ` Luis Henriques
2021-02-23 15:28 ` Amir Goldstein
2021-02-23 15:29 ` dai.ngo
2021-02-23 16:02 ` dai.ngo
2021-02-23 16:47 ` Amir Goldstein
2021-02-23 16:57 ` dai.ngo
[not found] ` <e3eed18b-fc7e-e687-608b-7f662017329c@oracle.com>
2021-02-23 17:33 ` Amir Goldstein
2021-02-24 0:13 ` dai.ngo
2021-02-23 17:56 ` Luis Henriques
2021-02-23 17:13 ` Olga Kornievskaia
2021-02-24 1:00 ` Olga Kornievskaia
2021-02-24 10:23 ` Luis Henriques
2021-02-24 10:44 ` Nicolas Boichat
2021-04-09 5:23 ` Nicolas Boichat
2021-04-09 13:39 ` Luis Henriques
2021-04-09 13:50 ` Amir Goldstein
2021-04-23 4:40 ` Nicolas Boichat
2021-05-03 8:54 ` Luis Henriques
2021-02-24 14:23 ` [PATCH] copy_file_range.2: Kernel v5.12 updates Luis Henriques
2021-02-24 16:10 ` Amir Goldstein
2021-02-25 10:21 ` Luis Henriques
2021-02-26 10:13 ` Alejandro Colomar (man-pages)
2021-02-26 10:34 ` Amir Goldstein
2021-02-26 11:15 ` Alejandro Colomar (man-pages)
2021-02-26 13:59 ` Jeff Layton
2021-02-26 21:26 ` Alejandro Colomar (man-pages)
2021-02-26 22:18 ` Alejandro Colomar (man-pages)
2021-02-27 5:41 ` Amir Goldstein
2021-02-27 12:20 ` Alejandro Colomar (man-pages)
2021-02-27 13:49 ` [RFC v2] copy_file_range.2: Update cross-filesystem support for 5.12 Alejandro Colomar
2021-02-27 16:00 ` Amir Goldstein
2021-02-27 23:08 ` [PATCH] copy_file_range.2: Kernel v5.12 updates Steve French
2021-02-28 7:35 ` Amir Goldstein
2021-02-28 22:25 ` Steve French
2021-03-01 6:18 ` Amir Goldstein
2021-03-01 14:41 ` [RFC v3] copy_file_range.2: Update cross-filesystem support for 5.12 Alejandro Colomar
2021-03-01 14:58 ` Amir Goldstein
2021-03-04 9:38 ` [RFC v4] " Alejandro Colomar
2021-03-04 17:13 ` Darrick J. Wong
2021-03-04 18:24 ` Alejandro Colomar (man-pages)
2021-03-04 23:50 ` Darrick J. Wong
2021-02-18 20:41 ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Steve French
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