xfs: fix unaligned access to rmapbt high keys in scrub
Subsystems (2)
PATCH v3 1/1 xfs: fix unaligned access to rmapbt high keys in scrub
The high keys in a rmapbt node block aren't naturally aligned. xchk_rmapbt_check_unwritten_in_keyflags() reads rm_offset through union xfs_btree_key and the union is 8-byte aligned.
The compiler may use an 8-byte load, and on sparc64 each high key takes an unaligned access trap:
Kernel unaligned access at TPC[105a54d8] xchk_rmapbt_check_unwritten_in_keyflags+0xb8/0x160 [xfs]
Read the keys through the packed struct xfs_rmap_key instead. This tells the compiler they may be unaligned. Decode rm_offset with be64_to_cpu() and drop the byte-swapped flag.
---
Tested on sparc64 (T4, 7.3.4) by scrubbing the rmapbt of a loop-mounted
image: alignment faults per scrub went from about 4000 to 0.
v3: separate key and rkey variables plus a comment (Dave), shorter changelog.
v2: https://lore.kernel.org/all/[email protected]/
v1: https://lore.kernel.org/all/[email protected]/
fs/xfs/scrub/rmap.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-)
fs/xfs/scrub/rmap.c +14 -7
@@ -149,8 +149,6 @@ xchk_rmapbt_check_unwritten_in_keyflags(struct xfs_scrub *sc = bs->sc;struct xfs_btree_cur *cur = bs->cur;struct xfs_btree_block *keyblock; -union xfs_btree_key *lkey, *hkey; -__be64 badflag =cpu_to_be64 (XFS_RMAP_OFF_UNWRITTEN );unsigned int level;if (sc->sm->sm_flags &XFS_SCRUB_OFLAG_PREEN )
@@ -159,6 +157,14 @@ xchk_rmapbt_check_unwritten_in_keyflags(for (level =1 ; level < cur->bc_nlevels; level++) {struct xfs_buf *bp;unsigned int ptr; +/* +* The on-disk high keys in an rmap node block are not +* naturally aligned, so decode them through the packed +* struct xfs_rmap_key to make the compiler treat them as +* unaligned. +*/ +union xfs_btree_key *key; +const struct xfs_rmap_key *rkey;/* Only check the first time we've seen this node block. */ if (cur->bc_levels[level].ptr >1 )
@@ -166,15 +172,16 @@ xchk_rmapbt_check_unwritten_in_keyflags( keyblock =xfs_btree_get_block (cur, level, &bp);for (ptr =1 ; ptr <=be16_to_cpu (keyblock->bb_numrecs); ptr++) { - lkey =xfs_btree_key_addr (cur, ptr, keyblock); - -if (lkey->rmap.rm_offset & badflag) { + key =xfs_btree_key_addr (cur, ptr, keyblock); + rkey = &key->rmap; +if (be64_to_cpu (rkey->rm_offset) &XFS_RMAP_OFF_UNWRITTEN ) {xchk_btree_set_preen (sc, cur, level);break ; } - hkey =xfs_btree_high_key_addr (cur, ptr, keyblock); -if (hkey->rmap.rm_offset & badflag) { + key =xfs_btree_high_key_addr (cur, ptr, keyblock); + rkey = &key->rmap; +if (be64_to_cpu (rkey->rm_offset) &XFS_RMAP_OFF_UNWRITTEN ) {xchk_btree_set_preen (sc, cur, level);break ; }
Signature · 1 line
2.43.0