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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>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"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>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"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?


  reply	other threads:[~2021-02-16 11:30 UTC|newest]

Thread overview: 136+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-12  4:43 [PATCH 0/6] Add generated flag to filesystem struct to block copy_file_range Nicolas Boichat
2021-02-12  4:44 ` [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated Nicolas Boichat
2021-02-12  7:46   ` Greg KH
2021-02-12  8:20     ` Nicolas Boichat
2021-02-12  8:37       ` Greg KH
2021-02-12 15:33         ` Ian Lance Taylor
2021-02-12 15:45           ` Greg KH
2021-02-12 15:59             ` Ian Lance Taylor
2021-02-12 16:28               ` Greg KH
2021-02-12 20:22                 ` Ian Lance Taylor
2021-02-12 23:03             ` Dave Chinner
2021-02-12 23:07               ` Ian Lance Taylor
2021-02-12 23:27                 ` Dave Chinner
2021-02-12 23:54                   ` Darrick J. Wong
2021-02-15  0:38                     ` Dave Chinner
2021-02-15  1:12                       ` Ian Lance Taylor
2021-02-15  1:25                         ` Nicolas Boichat
2021-02-15  5:56                           ` Amir Goldstein
2021-02-15  8:30                           ` Greg KH
2021-02-12  8:22     ` Amir Goldstein
2021-02-12  8:39       ` Greg KH
2021-02-12 12:05         ` Luis Henriques
2021-02-12 12:18           ` Greg KH
2021-02-12 12:41             ` Luis Henriques
2021-02-12 14:11               ` Greg KH
2021-02-12 15:01                 ` Luis Henriques
2021-02-15  6:12               ` Amir Goldstein
2021-02-15 10:39                 ` Luis Henriques
2021-02-15 12:22                   ` Luis Henriques
2021-02-15 14:23                     ` Amir Goldstein
2021-02-15 14:51                       ` Luis Henriques
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
2021-05-10  4:59                                                                     ` Amir Goldstein
2021-05-10  9:10                                                                       ` 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
2021-02-24  7:15                                     ` [PATCH v4] vfs: fix copy_file_range regression in cross-fs copies Amir Goldstein
2021-02-24  8:30                                       ` Petr Vorel
2021-02-18 20:41                             ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Steve French
2021-02-12 23:15       ` [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated Dave Chinner
2021-02-12  7:54   ` Amir Goldstein
2021-02-12  4:44 ` [PATCH 2/6] proc: Add FS_GENERATED_CONTENT to filesystem flags Nicolas Boichat
2021-02-12  4:44 ` [PATCH 6/6] vfs: Disallow copy_file_range on generated file systems Nicolas Boichat
2021-02-12  4:53   ` Darrick J. Wong
2021-02-12  4:59     ` Darrick J. Wong
2021-02-12  5:24       ` Nicolas Boichat
2021-02-14 23:09 ` [PATCH 0/6] Add generated flag to filesystem struct to block copy_file_range Al Viro

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