On Thu, Mar 06, 2025 at 04:45:06PM -0800, Luis Chamberlain wrote:
> On Thu, Mar 06, 2025 at 01:39:49PM -0500, Kent Overstreet wrote:
> > On Tue, Mar 04, 2025 at 05:53:01PM -0800, Luis Chamberlain wrote:
> > > The commit titled "block/bdev: lift block size restrictions to 64k"
> > > lifted the block layer's max supported block size to 64k inside the
> > > helper blk_validate_block_size() now that we support large folios.
> > > However in lifting the block size we also removed the silly use
> > > cases many filesystems have to use sb_set_blocksize() to *verify*
> > > that the block size < PAGE_SIZE. The call to sb_set_blocksize() can
> > > happen in-kernel given mkfs utilities *can* create for example an
> > > ext4 32k block size filesystem on x86_64, the issue we want to prevent
> > > is mounting it on x86_64 unless the filesystem supports LBS.
> > >
> > > While, we could argue that such checks should be filesystem specific,
> > > there are much more users of sb_set_blocksize() than LBS enabled
> > > filesystem on linux-next, so just do the easier thing and bring back
> > > the PAGE_SIZE check for sb_set_blocksize() users.
> > >
> > > This will ensure that tests such as generic/466 when run in a loop
> > > against say, ext4, won't try to try to actually mount a filesystem with
> > > a block size larger than your filesystem supports given your PAGE_SIZE
> > > and in the worst case crash.
> > >
> > > Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> > > Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> >
> > bcachefs doesn't use sb_set_blocksize() - but it appears it should, and
> > it does also support bs > ps in -next.
> >
> > Can we get a proper helper for lbs filesystems?
>
> What do you think of this last recommention I had?
Perfect :)
>
> diff --git a/block/bdev.c b/block/bdev.c
> index 3bd948e6438d..4844d1e27b6f 100644
> --- a/block/bdev.c
> +++ b/block/bdev.c
> @@ -181,6 +181,8 @@ EXPORT_SYMBOL(set_blocksize);
>
> int sb_set_blocksize(struct super_block *sb, int size)
> {
> + if (!(sb->s_type->fs_flags & FS_LBS) && size > PAGE_SIZE)
> + return 0;
> if (set_blocksize(sb->s_bdev_file, size))
> return 0;
> /* If we get here, we know size is validated */
> diff --git a/fs/bcachefs/fs.c b/fs/bcachefs/fs.c
> index 90ade8f648d9..e99e378d68ea 100644
> --- a/fs/bcachefs/fs.c
> +++ b/fs/bcachefs/fs.c
> @@ -2396,7 +2396,7 @@ static struct file_system_type bcache_fs_type = {
> .name = "bcachefs",
> .init_fs_context = bch2_init_fs_context,
> .kill_sb = bch2_kill_sb,
> - .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
> + .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_LBS,
> };
>
> MODULE_ALIAS_FS("bcachefs");
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index d92d7a07ea89..3d8b80165d48 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -2118,7 +2118,8 @@ static struct file_system_type xfs_fs_type = {
> .init_fs_context = xfs_init_fs_context,
> .parameters = xfs_fs_parameters,
> .kill_sb = xfs_kill_sb,
> - .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_MGTIME,
> + .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_MGTIME |
> + FS_LBS,
> };
> MODULE_ALIAS_FS("xfs");
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 2c3b2f8a621f..16d17bd82be0 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2616,6 +2616,7 @@ struct file_system_type {
> #define FS_DISALLOW_NOTIFY_PERM 16 /* Disable fanotify permission events */
> #define FS_ALLOW_IDMAP 32 /* FS has been updated to handle vfs idmappings. */
> #define FS_MGTIME 64 /* FS uses multigrain timestamps */
> +#define FS_LBS 128 /* FS supports LBS */
> #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
> int (*init_fs_context)(struct fs_context *);
> const struct fs_parameter_spec *parameters;
