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References: <20221117205249.1886336-1-amir73il@gmail.com>
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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Thu, 24 Nov 2022 11:54:20 +0200
Message-ID: <CAOQ4uxhzuZ+5+ZARwRLrZhz7tVt19AST982CEpZnUaKGuBokcw@mail.gmail.com>
Subject: Re: [PATCH v2] vfs: fix copy_file_range() averts filesystem freeze protection
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        Namjae Jeon <linkinjeon@kernel.org>,
        Luis Henriques <lhenriques@suse.com>,
        Olga Kornievskaia <olga.kornievskaia@gmail.com>,
        Jan Kara <jack@suse.cz>, linux-fsdevel@vger.kernel.org,
        linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org,
        Luis Henriques <lhenriques@suse.de>
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On Thu, Nov 17, 2022 at 10:53 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> Commit 868f9f2f8e00 ("vfs: fix copy_file_range() regression in cross-fs
> copies") removed fallback to generic_copy_file_range() for cross-fs
> cases inside vfs_copy_file_range().
>
> To preserve behavior of nfsd and ksmbd server-side-copy, the fallback to
> generic_copy_file_range() was added in nfsd and ksmbd code, but that
> call is missing sb_start_write(), fsnotify hooks and more.
>
> Ideally, nfsd and ksmbd would pass a flag to vfs_copy_file_range() that
> will take care of the fallback, but that code would be subtle and we got
> vfs_copy_file_range() logic wrong too many times already.
>
> Instead, add a flag to explicitly request vfs_copy_file_range() to
> perform only generic_copy_file_range() and let nfsd and ksmbd use this
> flag only in the fallback path.
>
> This choise keeps the logic changes to minimum in the non-nfsd/ksmbd code
> paths to reduce the risk of further regressions.
>
> Fixes: 868f9f2f8e00 ("vfs: fix copy_file_range() regression in cross-fs copies")
> Tested-by: Namjae Jeon <linkinjeon@kernel.org>
> Tested-by: Luis Henriques <lhenriques@suse.de>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>
> Hi Linus,
>
> I've tried Al, but he seems to be AFK, so since you ended up applying
> the regressing commit, I might as well send you the fix as well.
>
> I intentionally chose a fix "for dummies", because I'd like to end this
> copy_file_range() regression streak.
>
> I ran the copy_range fstests group on ext4/xfs/overlay to verify no
> regressions in local fs and nfsv3/nfsv4 to test server-side-copy.
>
> I also patched copy_file_range() locally to test the "dumb" fallback
> code on local fs.
>
> Namje tested ksmbd.
>
> Please apply.
>

Ping.

Happy Thanksgiving!
Amir.

>
> Changes since v1:
> - Added Tested-by's
>
>  fs/ksmbd/vfs.c     |  6 +++---
>  fs/nfsd/vfs.c      |  4 ++--
>  fs/read_write.c    | 19 +++++++++++++++----
>  include/linux/fs.h |  8 ++++++++
>  4 files changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/fs/ksmbd/vfs.c b/fs/ksmbd/vfs.c
> index 8de970d6146f..94b8ed4ef870 100644
> --- a/fs/ksmbd/vfs.c
> +++ b/fs/ksmbd/vfs.c
> @@ -1794,9 +1794,9 @@ int ksmbd_vfs_copy_file_ranges(struct ksmbd_work *work,
>                 ret = vfs_copy_file_range(src_fp->filp, src_off,
>                                           dst_fp->filp, dst_off, len, 0);
>                 if (ret == -EOPNOTSUPP || ret == -EXDEV)
> -                       ret = generic_copy_file_range(src_fp->filp, src_off,
> -                                                     dst_fp->filp, dst_off,
> -                                                     len, 0);
> +                       ret = vfs_copy_file_range(src_fp->filp, src_off,
> +                                                 dst_fp->filp, dst_off, len,
> +                                                 COPY_FILE_SPLICE);
>                 if (ret < 0)
>                         return ret;
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index f650afedd67f..5cf11cde51f8 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -596,8 +596,8 @@ ssize_t nfsd_copy_file_range(struct file *src, u64 src_pos, struct file *dst,
>         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);
> +               ret = vfs_copy_file_range(src, src_pos, dst, dst_pos, count,
> +                                         COPY_FILE_SPLICE);
>         return ret;
>  }
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 328ce8cf9a85..24b9668d6377 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1388,6 +1388,8 @@ ssize_t generic_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)
>  {
> +       lockdep_assert(sb_write_started(file_inode(file_out)->i_sb));
> +
>         return do_splice_direct(file_in, &pos_in, file_out, &pos_out,
>                                 len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0);
>  }
> @@ -1424,7 +1426,9 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
>          * and several different sets of file_operations, but they all end up
>          * using the same ->copy_file_range() function pointer.
>          */
> -       if (file_out->f_op->copy_file_range) {
> +       if (flags & COPY_FILE_SPLICE) {
> +               /* cross sb splice is allowed */
> +       } else 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;
> @@ -1474,8 +1478,9 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>                             size_t len, unsigned int flags)
>  {
>         ssize_t ret;
> +       bool splice = flags & COPY_FILE_SPLICE;
>
> -       if (flags != 0)
> +       if (flags & ~COPY_FILE_SPLICE)
>                 return -EINVAL;
>
>         ret = generic_copy_file_checks(file_in, pos_in, file_out, pos_out, &len,
> @@ -1501,14 +1506,14 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>          * same sb using clone, but for filesystems where both clone and copy
>          * are supported (e.g. nfs,cifs), we only call the copy method.
>          */
> -       if (file_out->f_op->copy_file_range) {
> +       if (!splice && 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);
>                 goto done;
>         }
>
> -       if (file_in->f_op->remap_file_range &&
> +       if (!splice && file_in->f_op->remap_file_range &&
>             file_inode(file_in)->i_sb == file_inode(file_out)->i_sb) {
>                 ret = file_in->f_op->remap_file_range(file_in, pos_in,
>                                 file_out, pos_out,
> @@ -1528,6 +1533,8 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>          * consistent story about which filesystems support copy_file_range()
>          * and which filesystems do not, that will allow userspace tools to
>          * make consistent desicions w.r.t using copy_file_range().
> +        *
> +        * We also get here if caller (e.g. nfsd) requested COPY_FILE_SPLICE.
>          */
>         ret = generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
>                                       flags);
> @@ -1582,6 +1589,10 @@ SYSCALL_DEFINE6(copy_file_range, int, fd_in, loff_t __user *, off_in,
>                 pos_out = f_out.file->f_pos;
>         }
>
> +       ret = -EINVAL;
> +       if (flags != 0)
> +               goto out;
> +
>         ret = vfs_copy_file_range(f_in.file, pos_in, f_out.file, pos_out, len,
>                                   flags);
>         if (ret > 0) {
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e654435f1651..59ae95ddb679 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2089,6 +2089,14 @@ struct dir_context {
>   */
>  #define REMAP_FILE_ADVISORY            (REMAP_FILE_CAN_SHORTEN)
>
> +/*
> + * These flags control the behavior of vfs_copy_file_range().
> + * They are not available to the user via syscall.
> + *
> + * COPY_FILE_SPLICE: call splice direct instead of fs clone/copy ops
> + */
> +#define COPY_FILE_SPLICE               (1 << 0)
> +
>  struct iov_iter;
>  struct io_uring_cmd;
>
> --
> 2.25.1
>