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From: dai.ngo@oracle.com
To: Luis Henriques <lhenriques@suse.de>
Cc: Amir Goldstein <amir73il@gmail.com>,
	Jeff Layton <jlayton@kernel.org>,
	Steve French <sfrench@samba.org>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Dave Chinner <dchinner@redhat.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Nicolas Boichat <drinkcat@chromium.org>,
	Ian Lance Taylor <iant@google.com>,
	Luis Lozano <llozano@chromium.org>,
	Andreas Dilger <adilger@dilger.ca>,
	Olga Kornievskaia <aglo@umich.edu>,
	Christoph Hellwig <hch@infradead.org>,
	ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-cifs@vger.kernel.org, samba-technical@lists.samba.org,
	linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org
Subject: Re: [PATCH v8] vfs: fix copy_file_range regression in cross-fs copies
Date: Tue, 23 Feb 2021 08:02:03 -0800	[thread overview]
Message-ID: <7c12e6a3-e4a6-5210-1b57-09072eac3270@oracle.com> (raw)
In-Reply-To: <7cc69c24-80dd-0053-24b9-3a28b0153f7e@oracle.com>


On 2/23/21 7:29 AM, dai.ngo@oracle.com wrote:
>
> On 2/23/21 2:32 AM, Luis Henriques wrote:
>> On Mon, Feb 22, 2021 at 08:25:27AM -0800, dai.ngo@oracle.com wrote:
>>> On 2/22/21 2:24 AM, Luis Henriques wrote:
>>>> A regression has been reported by Nicolas Boichat, found while 
>>>> using the
>>>> copy_file_range syscall to copy a tracefs file.  Before commit
>>>> 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices") the
>>>> kernel would return -EXDEV to userspace when trying to copy a file 
>>>> across
>>>> different filesystems.  After this commit, the syscall doesn't fail 
>>>> anymore
>>>> and instead returns zero (zero bytes copied), as this file's 
>>>> content is
>>>> generated on-the-fly and thus reports a size of zero.
>>>>
>>>> This patch restores some cross-filesystem copy restrictions that 
>>>> existed
>>>> prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy 
>>>> across
>>>> devices").  Filesystems are still allowed to fall-back to the VFS
>>>> generic_copy_file_range() implementation, but that has now to be done
>>>> explicitly.
>>>>
>>>> nfsd is also modified to fall-back into generic_copy_file_range() 
>>>> in case
>>>> vfs_copy_file_range() fails with -EOPNOTSUPP or -EXDEV.
>>>>
>>>> Fixes: 5dae222a5ff0 ("vfs: allow copy_file_range to copy across 
>>>> devices")
>>>> Link: 
>>>> https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@chromium.org/__;!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmi49dC6w$
>>>> Link: 
>>>> https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx*BnvW=ZmpsG47CyHFJwnw7zSX6Q@mail.gmail.com/__;Kw!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmgCmMHzA$
>>>> Link: 
>>>> https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/__;!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmzqItkrQ$
>>>> Reported-by: Nicolas Boichat <drinkcat@chromium.org>
>>>> Signed-off-by: Luis Henriques <lhenriques@suse.de>
>>>> ---
>>>> Changes since v7
>>>> - set 'ret' to '-EOPNOTSUPP' before the clone 'if' statement so 
>>>> that the
>>>>     error returned is always related to the 'copy' operation
>>>> Changes since v6
>>>> - restored i_sb checks for the clone operation
>>>> Changes since v5
>>>> - check if ->copy_file_range is NULL before calling it
>>>> Changes since v4
>>>> - nfsd falls-back to generic_copy_file_range() only *if* it gets 
>>>> -EOPNOTSUPP
>>>>     or -EXDEV.
>>>> Changes since v3
>>>> - dropped the COPY_FILE_SPLICE flag
>>>> - kept the f_op's checks early in generic_copy_file_checks, 
>>>> implementing
>>>>     Amir's suggestions
>>>> - modified nfsd to use generic_copy_file_range()
>>>> Changes since v2
>>>> - do all the required checks earlier, in generic_copy_file_checks(),
>>>>     adding new checks for ->remap_file_range
>>>> - new COPY_FILE_SPLICE flag
>>>> - don't remove filesystem's fallback to generic_copy_file_range()
>>>> - updated commit changelog (and subject)
>>>> Changes since v1 (after Amir review)
>>>> - restored do_copy_file_range() helper
>>>> - return -EOPNOTSUPP if fs doesn't implement CFR
>>>> - updated commit description
>>>>
>>>>    fs/nfsd/vfs.c   |  8 +++++++-
>>>>    fs/read_write.c | 49 
>>>> ++++++++++++++++++++++++-------------------------
>>>>    2 files changed, 31 insertions(+), 26 deletions(-)
>>>>
>>>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
>>>> index 04937e51de56..23dab0fa9087 100644
>>>> --- a/fs/nfsd/vfs.c
>>>> +++ b/fs/nfsd/vfs.c
>>>> @@ -568,6 +568,7 @@ __be32 nfsd4_clone_file_range(struct nfsd_file 
>>>> *nf_src, u64 src_pos,
>>>>    ssize_t nfsd_copy_file_range(struct file *src, u64 src_pos, 
>>>> struct file *dst,
>>>>                     u64 dst_pos, u64 count)
>>>>    {
>>>> +    ssize_t ret;
>>>>        /*
>>>>         * Limit copy to 4MB to prevent indefinitely blocking an nfsd
>>>> @@ -578,7 +579,12 @@ ssize_t nfsd_copy_file_range(struct file *src, 
>>>> u64 src_pos, struct file *dst,
>>>>         * 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);
>>>> +    ret = vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);
>>>> +
>>>> +    if (ret == -EOPNOTSUPP || ret == -EXDEV)
>>>> +        ret = generic_copy_file_range(src, src_pos, dst, dst_pos,
>>>> +                          count, 0);
>>>> +    return ret;
>>>>    }
>>>>    __be32 nfsd4_vfs_fallocate(struct svc_rqst *rqstp, struct svc_fh 
>>>> *fhp,
>>>> diff --git a/fs/read_write.c b/fs/read_write.c
>>>> index 75f764b43418..5a26297fd410 100644
>>>> --- a/fs/read_write.c
>>>> +++ b/fs/read_write.c
>>>> @@ -1388,28 +1388,6 @@ ssize_t generic_copy_file_range(struct file 
>>>> *file_in, loff_t pos_in,
>>>>    }
>>>>    EXPORT_SYMBOL(generic_copy_file_range);
>>>> -static ssize_t do_copy_file_range(struct file *file_in, loff_t 
>>>> pos_in,
>>>> -                  struct file *file_out, loff_t pos_out,
>>>> -                  size_t len, unsigned int flags)
>>>> -{
>>>> -    /*
>>>> -     * Although we now allow filesystems to handle cross sb copy, 
>>>> passing
>>>> -     * a file of the wrong filesystem type to filesystem driver 
>>>> can result
>>>> -     * in an attempt to dereference the wrong type of 
>>>> ->private_data, so
>>>> -     * avoid doing that until we really have a good reason.  NFS 
>>>> defines
>>>> -     * several different file_system_type structures, but they all 
>>>> end up
>>>> -     * using the same ->copy_file_range() function pointer.
>>>> -     */
>>>> -    if (file_out->f_op->copy_file_range &&
>>>> -        file_out->f_op->copy_file_range == 
>>>> file_in->f_op->copy_file_range)
>>>> -        return file_out->f_op->copy_file_range(file_in, pos_in,
>>>> -                               file_out, pos_out,
>>>> -                               len, flags);
>>>> -
>>>> -    return generic_copy_file_range(file_in, pos_in, file_out, 
>>>> pos_out, len,
>>>> -                       flags);
>>>> -}
>>>> -
>>>>    /*
>>>>     * Performs necessary checks before doing a file copy
>>>>     *
>>>> @@ -1427,6 +1405,25 @@ static int generic_copy_file_checks(struct 
>>>> file *file_in, loff_t pos_in,
>>>>        loff_t size_in;
>>>>        int ret;
>>>> +    /*
>>>> +     * Although we now allow filesystems to handle cross sb copy, 
>>>> passing
>>>> +     * a file of the wrong filesystem type to filesystem driver 
>>>> can result
>>>> +     * in an attempt to dereference the wrong type of 
>>>> ->private_data, so
>>>> +     * avoid doing that until we really have a good reason.  NFS 
>>>> defines
>>>> +     * several different file_system_type structures, but they all 
>>>> end up
>>>> +     * using the same ->copy_file_range() function pointer.
>>>> +     */
>>>> +    if (file_out->f_op->copy_file_range) {
>>>> +        if (file_in->f_op->copy_file_range !=
>>>> +            file_out->f_op->copy_file_range)
>>>> +            return -EXDEV;
>>>> +    } else if (file_in->f_op->remap_file_range) {
>>>> +        if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
>>>> +            return -EXDEV;
>>> I think this check is redundant, it's done in vfs_copy_file_range.
>>> If this check is removed then the else clause below should be removed
>>> also. Once this check and the else clause are removed then might as
>>> well move the the check of copy_file_range from here to 
>>> vfs_copy_file_range.
>>>
>> I don't think it's really redundant, although I agree is messy due to 
>> the
>> fact we try to clone first instead of copying them.
>>
>> So, in the clone path, this is the only place where we return -EXDEV if:
>>
>> 1) we don't have ->copy_file_range *and*
>> 2) we have ->remap_file_range but the i_sb are different.
>>
>> The check in vfs_copy_file_range() is only executed if:
>>
>> 1) we have *valid* ->copy_file_range ops and/or
>> 2) we have *valid* ->remap_file_range
>>
>> So... if we remove the check in generic_copy_file_checks() as you 
>> suggest
>> and:
>> - we don't have ->copy_file_range,
>> - we have ->remap_file_range but
>> - the i_sb are different
>>
>> we'll return the -EOPNOTSUPP (the one set in line "ret = 
>> -EOPNOTSUPP;" in
>> function vfs_copy_file_range() ) instead of -EXDEV.
>
> Yes, this is the different.The NFS code handles both -EOPNOTSUPP and
> -EXDEVV by doing generic_copy_file_range.  Do any other consumers of
> vfs_copy_file_range rely on -EXDEV and not -EOPNOTSUPP and which is
> the correct error code for this case? It seems to me that -EOPNOTSUPP
> is more appropriate than EXDEV when (sb1 != sb2).

So with the current patch, for a clone operation across 2 filesystems:

   . if src and dst filesystem support both copy_file_range and
     map_file_range then the code returns -ENOTSUPPORT.

   . if the filesystems only support map_file_range then the
     code returns -EXDEV

This seems confusing, shouldn't only 1 error code returned for this case?

-Dai

>
>>
>> But I may have got it all wrong.  I've looked so many times at this code
>> that I'm probably useless at finding problems in it :-)
>
> You're not alone, we all try to do the right thing :-)
>
> -Dai
>
>>
>> Cheers,
>> -- 
>> Luís
>>
>>> -Dai
>>>
>>>> +    } else {
>>>> +                return -EOPNOTSUPP;
>>>> +    }
>>>> +
>>>>        ret = generic_file_rw_checks(file_in, file_out);
>>>>        if (ret)
>>>>            return ret;
>>>> @@ -1495,6 +1492,7 @@ ssize_t vfs_copy_file_range(struct file 
>>>> *file_in, loff_t pos_in,
>>>>        file_start_write(file_out);
>>>> +    ret = -EOPNOTSUPP;
>>>>        /*
>>>>         * Try cloning first, this is supported by more file 
>>>> systems, and
>>>>         * more efficient if both clone and copy are supported (e.g. 
>>>> NFS).
>>>> @@ -1513,9 +1511,10 @@ ssize_t vfs_copy_file_range(struct file 
>>>> *file_in, loff_t pos_in,
>>>>            }
>>>>        }
>>>> -    ret = do_copy_file_range(file_in, pos_in, file_out, pos_out, len,
>>>> -                flags);
>>>> -    WARN_ON_ONCE(ret == -EOPNOTSUPP);
>>>> +    if (file_out->f_op->copy_file_range)
>>>> +        ret = file_out->f_op->copy_file_range(file_in, pos_in,
>>>> +                              file_out, pos_out,
>>>> +                              len, flags);
>>>>    done:
>>>>        if (ret > 0) {
>>>>            fsnotify_access(file_in);

  reply	other threads:[~2021-02-23 16:04 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
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 [this message]
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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