On Oct 1, 2014, at 3:33 PM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote:
> Delalloc write journal reservations only reserve 1 credit,
> to update the inode if necessary. However, it may happen
> once in a filesystem's lifetime that a file will cross
> the 2G threshold, and require the LARGE_FILE feature to
> be set in the superblock as well, if it was not set already.
>
> This overruns the transaction reservation, and can be
> demonstrated simply on any ext4 filesystem without the LARGE_FILE
> feature already set:
>
> dd if=/dev/zero of=testfile bs=1 seek=2147483646 count=1 \
> conv=notrunc of=testfile
> sync
> dd if=/dev/zero of=testfile bs=1 seek=2147483647 count=1 \
> conv=notrunc of=testfile
>
> leads to:
>
> EXT4-fs: ext4_do_update_inode:4296: aborting transaction: error 28 in __ext4_handle_dirty_super
> EXT4-fs error (device loop0) in ext4_do_update_inode:4301: error 28
> EXT4-fs error (device loop0) in ext4_reserve_inode_write:4757: Readonly filesystem
> EXT4-fs error (device loop0) in ext4_dirty_inode:4876: error 28
> EXT4-fs error (device loop0) in ext4_da_write_end:2685: error 28
>
> It simplifies things if we ensure that when we are running
> with delalloc, we have LARGE_FILE set already; that way we
> don't have to potentially set it later during a file write.
>
> For any fs of sufficient size, LARGE_FILE is usually set
> simply due to the size of the resize inode. And for ext4,
> HUGE_FILE is set by default.
>
> LARGE_FILE is a decades-old compatibility flag, so at this
> point there is little risk of backwards compatibility problems
> by enabling it when the filesystem is mounted as ext4.
>
> So just set LARGE_FILE if we are mounted delalloc, if it's
> not set already, and be done with it.
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 0b28b36..8e56d7e 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3576,6 +3576,20 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> clear_opt(sb, DELALLOC);
> }
>
> + /*
> + * Adding the LARGE_FILES feature to the superblock adds
> + * unnecessary complication to journal credit calculations
> + * when delalloc is enabled. This is a decades-old feature,
> + * so just enable it now to simplify things.
> + */
> + if (test_opt(sb, DELALLOC) && !(sb->s_flags & MS_RDONLY) &&
> + EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_HAS_JOURNAL) &&
> + !EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_LARGE_FILE)) {
> + ext4_update_dynamic_rev(sb);
> + EXT4_SET_RO_COMPAT_FEATURE(sb,
> + EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
This sets the superblock flag, but doesn't actually mark the superblock
dirty. Later in ext4_fill_super() it is possible that this buffer_head
is discarded without writing it out:
if (sb->s_blocksize != blocksize) {
:
:
brelse(bh);
While this isn't completely fatal (the next mount would enable this
flag again), it could cause some errors to appear in e2fsck if large
files are created without the large_file feature in the superblock.
It would probably be safer to mark the superblock dirty in this case
so that it is written out. No need to sync it I think
ext4_commit_super(sb, 0);
Also, it looks like it is possible to enable delalloc via remount, so
this feature check/set should also be added there?
Cheers, Andreas
> + }
> +
> sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
> (test_opt(sb, POSIX_ACL) ? MS_POSIXACL : 0);
>
>
> --
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Cheers, Andreas
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