Re: [PATCH 3/3] xfs: sanitise sb_bad_features2 handling

Brian Foster
2015-01-08T14:36:47Z

On Thu, Jan 08, 2015 at 08:51:05AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> We currently have to ensure that every time we update sb_features2
> that we update sb_bad_features2. Now that we log and format the
> superblock in it's entirety we actually don't have to care because
> we can simply update the sb_bad_features2 when we format it into the
> buffer. This removes the need for anything but the mount and
> superblock formatting code to care about sb_bad_features2, and
> hence removes the possibility that we forget to update bad_features2
> when necessary in the future.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

> fs/xfs/libxfs/xfs_format.h | 14 +++++++-------
> fs/xfs/libxfs/xfs_sb.c | 8 +++++++-
> fs/xfs/xfs_mount.c | 23 +++++++++++------------
> 3 files changed, 25 insertions(+), 20 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index 4762732..8eb7189 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -151,10 +151,13 @@ typedef struct xfs_sb {
> __uint32_t sb_features2; /* additional feature bits */
>
> /*
> - * bad features2 field as a result of failing to pad the sb
> - * structure to 64 bits. Some machines will be using this field
> - * for features2 bits. Easiest just to mark it bad and not use
> - * it for anything else.
> + * bad features2 field as a result of failing to pad the sb structure to
> + * 64 bits. Some machines will be using this field for features2 bits.
> + * Easiest just to mark it bad and not use it for anything else.
> + *
> + * This is not kept up to date in memory; it is always overwritten by
> + * the value in sb_features2 when formatting the incore superblock to
> + * the disk buffer.
> */
> __uint32_t sb_bad_features2;
>
> @@ -453,13 +456,11 @@ static inline void xfs_sb_version_addattr2(struct xfs_sb *sbp)
> {
> sbp->sb_versionnum |= XFS_SB_VERSION_MOREBITSBIT;
> sbp->sb_features2 |= XFS_SB_VERSION2_ATTR2BIT;
> - sbp->sb_bad_features2 |= XFS_SB_VERSION2_ATTR2BIT;
> }
>
> static inline void xfs_sb_version_removeattr2(struct xfs_sb *sbp)
> {
> sbp->sb_features2 &= ~XFS_SB_VERSION2_ATTR2BIT;
> - sbp->sb_bad_features2 &= ~XFS_SB_VERSION2_ATTR2BIT;
> if (!sbp->sb_features2)
> sbp->sb_versionnum &= ~XFS_SB_VERSION_MOREBITSBIT;
> }
> @@ -475,7 +476,6 @@ static inline void xfs_sb_version_addprojid32bit(struct xfs_sb *sbp)
> {
> sbp->sb_versionnum |= XFS_SB_VERSION_MOREBITSBIT;
> sbp->sb_features2 |= XFS_SB_VERSION2_PROJID32BIT;
> - sbp->sb_bad_features2 |= XFS_SB_VERSION2_PROJID32BIT;
> }
>
> /*
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index 6ee3af6..b440839 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -488,7 +488,6 @@ xfs_sb_to_disk(
> to->sb_fdblocks = cpu_to_be64(from->sb_fdblocks);
> to->sb_frextents = cpu_to_be64(from->sb_frextents);
>
> -
> to->sb_flags = from->sb_flags;
> to->sb_shared_vn = from->sb_shared_vn;
> to->sb_inoalignmt = cpu_to_be32(from->sb_inoalignmt);
> @@ -498,6 +497,13 @@ xfs_sb_to_disk(
> to->sb_logsectlog = from->sb_logsectlog;
> to->sb_logsectsize = cpu_to_be16(from->sb_logsectsize);
> to->sb_logsunit = cpu_to_be32(from->sb_logsunit);
> +
> + /*
> + * We need to ensure that bad_features2 always matches features2.
> + * Hence we enforce that here rather than having to remember to do it
> + * everywhere else that updates features2.
> + */
> + from->sb_bad_features2 = from->sb_features2;
> to->sb_features2 = cpu_to_be32(from->sb_features2);
> to->sb_bad_features2 = cpu_to_be32(from->sb_bad_features2);
>
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index 5ef9aa2..4fa80e6 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -640,25 +640,24 @@ xfs_mountfs(
> xfs_sb_mount_common(mp, sbp);
>
> /*
> - * Check for a mismatched features2 values. Older kernels
> - * read & wrote into the wrong sb offset for sb_features2
> - * on some platforms due to xfs_sb_t not being 64bit size aligned
> - * when sb_features2 was added, which made older superblock
> - * reading/writing routines swap it as a 64-bit value.
> + * Check for a mismatched features2 values. Older kernels read & wrote
> + * into the wrong sb offset for sb_features2 on some platforms due to
> + * xfs_sb_t not being 64bit size aligned when sb_features2 was added,
> + * which made older superblock reading/writing routines swap it as a
> + * 64-bit value.
> *
> * For backwards compatibility, we make both slots equal.
> *
> - * If we detect a mismatched field, we OR the set bits into the
> - * existing features2 field in case it has already been modified; we
> - * don't want to lose any features. We then update the bad location
> - * with the ORed value so that older kernels will see any features2
> - * flags, and mark the two fields as needing updates once the
> - * transaction subsystem is online.
> + * If we detect a mismatched field, we OR the set bits into the existing
> + * features2 field in case it has already been modified; we don't want
> + * to lose any features. We then update the bad location with the ORed
> + * value so that older kernels will see any features2 flags. The
> + * superblock writeback code ensures the new sb_features2 is copied to
> + * sb_bad_features2 before it is logged or written to disk.
> */
> if (xfs_sb_has_mismatched_features2(sbp)) {
> xfs_warn(mp, "correcting sb_features alignment problem");
> sbp->sb_features2 |= sbp->sb_bad_features2;
> - sbp->sb_bad_features2 = sbp->sb_features2;
> mp->m_update_sb = true;
>
> /*
> --
> 2.0.0
>
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