Re: [PATCH v2] vfs: fix copy_file_range() averts filesystem freeze protection

[Al Viro <viro@zeniv.linux.org.uk>]

On Thu, Nov 17, 2022 at 10:52:49PM +0200, Amir Goldstein 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>

Applied...