From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Increase XFS_BLF_DATAMAP_SIZE by 1 to fill in the implied padding at the
end of struct xfs_buf_log_format. This makes the size consistent so
that we can check it in xfs_ondisk.h, and will be needed once we start
logging attribute values.
On amd64 we get the following pahole:
struct xfs_buf_log_format {
short unsigned int blf_type; /* 0 2 */
short unsigned int blf_size; /* 2 2 */
short unsigned int blf_flags; /* 4 2 */
short unsigned int blf_len; /* 6 2 */
long long int blf_blkno; /* 8 8 */
unsigned int blf_map_size; /* 16 4 */
unsigned int blf_data_map[16]; /* 20 64 */
/* --- cacheline 1 boundary (64 bytes) was 20 bytes ago --- */
/* size: 88, cachelines: 2, members: 7 */
/* padding: 4 */
/* last cacheline: 24 bytes */
};
But on i386 we get the following:
struct xfs_buf_log_format {
short unsigned int blf_type; /* 0 2 */
short unsigned int blf_size; /* 2 2 */
short unsigned int blf_flags; /* 4 2 */
short unsigned int blf_len; /* 6 2 */
long long int blf_blkno; /* 8 8 */
unsigned int blf_map_size; /* 16 4 */
unsigned int blf_data_map[16]; /* 20 64 */
/* --- cacheline 1 boundary (64 bytes) was 20 bytes ago --- */
/* size: 84, cachelines: 2, members: 7 */
/* last cacheline: 20 bytes */
};
Notice how the amd64 compiler inserts 4 bytes of padding to the end of
the structure to ensure 8-byte alignment. Prior to "xfs: fix memory
corruption during remote attr value buffer invalidation" we would try to
write to blf_data_map[17], which is harmless on amd64 but really bad on
i386.
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
fs/xfs/libxfs/xfs_log_format.h | 19 ++++++++++++++-----
fs/xfs/xfs_ondisk.h | 1 +
2 files changed, 15 insertions(+), 5 deletions(-)
diff --git a/fs/xfs/libxfs/xfs_log_format.h b/fs/xfs/libxfs/xfs_log_format.h
index 8ef31d71a9c7..9bac0d2e56dc 100644
--- a/fs/xfs/libxfs/xfs_log_format.h
+++ b/fs/xfs/libxfs/xfs_log_format.h
@@ -462,11 +462,20 @@ static inline uint xfs_log_dinode_size(int version)
#define XFS_BLF_GDQUOT_BUF (1<<4)
/*
- * This is the structure used to lay out a buf log item in the
- * log. The data map describes which 128 byte chunks of the buffer
- * have been logged.
- */
-#define XFS_BLF_DATAMAP_SIZE ((XFS_MAX_BLOCKSIZE / XFS_BLF_CHUNK) / NBWORD)
+ * This is the structure used to lay out a buf log item in the log. The data
+ * map describes which 128 byte chunks of the buffer have been logged.
+ *
+ * The placement of blf_map_size causes blf_data_map to start at an odd
+ * multiple of sizeof(unsigned int) offset within the struct. Because the data
+ * bitmap size will always be an even number, the end of the data_map (and
+ * therefore the structure) will also be at an odd multiple of sizeof(unsigned
+ * int). Some 64-bit compilers will insert padding at the end of the struct to
+ * ensure 64-bit alignment of blf_blkno, but 32-bit ones will not. Therefore,
+ * XFS_BLF_DATAMAP_SIZE must be an odd number to make the padding explicit and
+ * keep the structure size consistent between 32-bit and 64-bit platforms.
+ */
+#define __XFS_BLF_DATAMAP_SIZE ((XFS_MAX_BLOCKSIZE / XFS_BLF_CHUNK) / NBWORD)
+#define XFS_BLF_DATAMAP_SIZE (__XFS_BLF_DATAMAP_SIZE + 1)
typedef struct xfs_buf_log_format {
unsigned short blf_type; /* buf log item type indicator */
diff --git a/fs/xfs/xfs_ondisk.h b/fs/xfs/xfs_ondisk.h
index b6701b4f59a9..5f04d8a5ab2a 100644
--- a/fs/xfs/xfs_ondisk.h
+++ b/fs/xfs/xfs_ondisk.h
@@ -111,6 +111,7 @@ xfs_check_ondisk_structs(void)
XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_hdr_t, 10);
/* log structures */
+ XFS_CHECK_STRUCT_SIZE(struct xfs_buf_log_format, 88);
XFS_CHECK_STRUCT_SIZE(struct xfs_dq_logformat, 24);
XFS_CHECK_STRUCT_SIZE(struct xfs_efd_log_format_32, 28);
XFS_CHECK_STRUCT_SIZE(struct xfs_efd_log_format_64, 32);
