From 64a39d876e77264dbd06ec27564d9e4eed1c6786 Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Tue, 29 May 2018 22:18:09 -0700 Subject: [PATCH] xfs: add helpers to collect and sift btree block pointers during repair Add some helpers to assemble a list of fs block extents. Generally, repair functions will iterate the rmapbt to make a list (1) of all extents owned by the nominal owner of the metadata structure; then they will iterate all other structures with the same rmap owner to make a list (2) of active blocks; and finally we have a subtraction function to subtract all the blocks in (2) from (1), with the result that (1) is now a list of blocks that were owned by the old btree and must be disposed. Signed-off-by: Darrick J. Wong Reviewed-by: Dave Chinner --- fs/xfs/scrub/repair.c | 217 ++++++++++++++++++++++++++++++++++++++++++ fs/xfs/scrub/repair.h | 28 ++++++ 2 files changed, 245 insertions(+) diff --git a/fs/xfs/scrub/repair.c b/fs/xfs/scrub/repair.c index be21a2984001..fca8e3c7887d 100644 --- a/fs/xfs/scrub/repair.c +++ b/fs/xfs/scrub/repair.c @@ -368,3 +368,220 @@ xfs_repair_init_btblock( return 0; } + +/* + * Reconstructing per-AG Btrees + * + * When a space btree is corrupt, we don't bother trying to fix it. Instead, + * we scan secondary space metadata to derive the records that should be in + * the damaged btree, initialize a fresh btree root, and insert the records. + * Note that for rebuilding the rmapbt we scan all the primary data to + * generate the new records. + * + * However, that leaves the matter of removing all the metadata describing the + * old broken structure. For primary metadata we use the rmap data to collect + * every extent with a matching rmap owner (exlist); we then iterate all other + * metadata structures with the same rmap owner to collect the extents that + * cannot be removed (sublist). We then subtract sublist from exlist to + * derive the blocks that were used by the old btree. These blocks can be + * reaped. + * + * For rmapbt reconstructions we must use different tactics for extent + * collection. First we iterate all primary metadata (this excludes the old + * rmapbt, obviously) to generate new rmap records. The gaps in the rmap + * records are collected as exlist. The bnobt records are collected as + * sublist. As with the other btrees we subtract sublist from exlist, and the + * result (since the rmapbt lives in the free space) are the blocks from the + * old rmapbt. + */ + +/* Collect a dead btree extent for later disposal. */ +int +xfs_repair_collect_btree_extent( + struct xfs_scrub_context *sc, + struct xfs_repair_extent_list *exlist, + xfs_fsblock_t fsbno, + xfs_extlen_t len) +{ + struct xfs_repair_extent *rex; + + trace_xfs_repair_collect_btree_extent(sc->mp, + XFS_FSB_TO_AGNO(sc->mp, fsbno), + XFS_FSB_TO_AGBNO(sc->mp, fsbno), len); + + rex = kmem_alloc(sizeof(struct xfs_repair_extent), KM_MAYFAIL); + if (!rex) + return -ENOMEM; + + INIT_LIST_HEAD(&rex->list); + rex->fsbno = fsbno; + rex->len = len; + list_add_tail(&rex->list, &exlist->list); + + return 0; +} + +/* + * An error happened during the rebuild so the transaction will be cancelled. + * The fs will shut down, and the administrator has to unmount and run repair. + * Therefore, free all the memory associated with the list so we can die. + */ +void +xfs_repair_cancel_btree_extents( + struct xfs_scrub_context *sc, + struct xfs_repair_extent_list *exlist) +{ + struct xfs_repair_extent *rex; + struct xfs_repair_extent *n; + + for_each_xfs_repair_extent_safe(rex, n, exlist) { + list_del(&rex->list); + kmem_free(rex); + } +} + +/* Compare two btree extents. */ +static int +xfs_repair_btree_extent_cmp( + void *priv, + struct list_head *a, + struct list_head *b) +{ + struct xfs_repair_extent *ap; + struct xfs_repair_extent *bp; + + ap = container_of(a, struct xfs_repair_extent, list); + bp = container_of(b, struct xfs_repair_extent, list); + + if (ap->fsbno > bp->fsbno) + return 1; + if (ap->fsbno < bp->fsbno) + return -1; + return 0; +} + +/* + * Remove all the blocks mentioned in @sublist from the extents in @exlist. + * + * The intent is that callers will iterate the rmapbt for all of its records + * for a given owner to generate @exlist; and iterate all the blocks of the + * metadata structures that are not being rebuilt and have the same rmapbt + * owner to generate @sublist. This routine subtracts all the extents + * mentioned in sublist from all the extents linked in @exlist, which leaves + * @exlist as the list of blocks that are not accounted for, which we assume + * are the dead blocks of the old metadata structure. The blocks mentioned in + * @exlist can be reaped. + */ +#define LEFT_ALIGNED (1 << 0) +#define RIGHT_ALIGNED (1 << 1) +int +xfs_repair_subtract_extents( + struct xfs_scrub_context *sc, + struct xfs_repair_extent_list *exlist, + struct xfs_repair_extent_list *sublist) +{ + struct list_head *lp; + struct xfs_repair_extent *ex; + struct xfs_repair_extent *newex; + struct xfs_repair_extent *subex; + xfs_fsblock_t sub_fsb; + xfs_extlen_t sub_len; + int state; + int error = 0; + + if (list_empty(&exlist->list) || list_empty(&sublist->list)) + return 0; + ASSERT(!list_empty(&sublist->list)); + + list_sort(NULL, &exlist->list, xfs_repair_btree_extent_cmp); + list_sort(NULL, &sublist->list, xfs_repair_btree_extent_cmp); + + /* + * Now that we've sorted both lists, we iterate exlist once, rolling + * forward through sublist and/or exlist as necessary until we find an + * overlap or reach the end of either list. We do not reset lp to the + * head of exlist nor do we reset subex to the head of sublist. The + * list traversal is similar to merge sort, but we're deleting + * instead. In this manner we avoid O(n^2) operations. + */ + subex = list_first_entry(&sublist->list, struct xfs_repair_extent, + list); + lp = exlist->list.next; + while (lp != &exlist->list) { + ex = list_entry(lp, struct xfs_repair_extent, list); + + /* + * Advance subex and/or ex until we find a pair that + * intersect or we run out of extents. + */ + while (subex->fsbno + subex->len <= ex->fsbno) { + if (list_is_last(&subex->list, &sublist->list)) + goto out; + subex = list_next_entry(subex, list); + } + if (subex->fsbno >= ex->fsbno + ex->len) { + lp = lp->next; + continue; + } + + /* trim subex to fit the extent we have */ + sub_fsb = subex->fsbno; + sub_len = subex->len; + if (subex->fsbno < ex->fsbno) { + sub_len -= ex->fsbno - subex->fsbno; + sub_fsb = ex->fsbno; + } + if (sub_len > ex->len) + sub_len = ex->len; + + state = 0; + if (sub_fsb == ex->fsbno) + state |= LEFT_ALIGNED; + if (sub_fsb + sub_len == ex->fsbno + ex->len) + state |= RIGHT_ALIGNED; + switch (state) { + case LEFT_ALIGNED: + /* Coincides with only the left. */ + ex->fsbno += sub_len; + ex->len -= sub_len; + break; + case RIGHT_ALIGNED: + /* Coincides with only the right. */ + ex->len -= sub_len; + lp = lp->next; + break; + case LEFT_ALIGNED | RIGHT_ALIGNED: + /* Total overlap, just delete ex. */ + lp = lp->next; + list_del(&ex->list); + kmem_free(ex); + break; + case 0: + /* + * Deleting from the middle: add the new right extent + * and then shrink the left extent. + */ + newex = kmem_alloc(sizeof(struct xfs_repair_extent), + KM_MAYFAIL); + if (!newex) { + error = -ENOMEM; + goto out; + } + INIT_LIST_HEAD(&newex->list); + newex->fsbno = sub_fsb + sub_len; + newex->len = ex->fsbno + ex->len - newex->fsbno; + list_add(&newex->list, &ex->list); + ex->len = sub_fsb - ex->fsbno; + lp = lp->next; + break; + default: + ASSERT(0); + break; + } + } + +out: + return error; +} +#undef LEFT_ALIGNED +#undef RIGHT_ALIGNED diff --git a/fs/xfs/scrub/repair.h b/fs/xfs/scrub/repair.h index 40990fa5f381..ba1fdd7b9a79 100644 --- a/fs/xfs/scrub/repair.h +++ b/fs/xfs/scrub/repair.h @@ -43,6 +43,34 @@ int xfs_repair_init_btblock(struct xfs_scrub_context *sc, xfs_fsblock_t fsb, struct xfs_buf **bpp, xfs_btnum_t btnum, const struct xfs_buf_ops *ops); +struct xfs_repair_extent { + struct list_head list; + xfs_fsblock_t fsbno; + xfs_extlen_t len; +}; + +struct xfs_repair_extent_list { + struct list_head list; +}; + +static inline void +xfs_repair_init_extent_list( + struct xfs_repair_extent_list *exlist) +{ + INIT_LIST_HEAD(&exlist->list); +} + +#define for_each_xfs_repair_extent_safe(rbe, n, exlist) \ + list_for_each_entry_safe((rbe), (n), &(exlist)->list, list) +int xfs_repair_collect_btree_extent(struct xfs_scrub_context *sc, + struct xfs_repair_extent_list *btlist, xfs_fsblock_t fsbno, + xfs_extlen_t len); +void xfs_repair_cancel_btree_extents(struct xfs_scrub_context *sc, + struct xfs_repair_extent_list *btlist); +int xfs_repair_subtract_extents(struct xfs_scrub_context *sc, + struct xfs_repair_extent_list *exlist, + struct xfs_repair_extent_list *sublist); + /* Metadata repairers */ int xfs_repair_probe(struct xfs_scrub_context *sc); -- GitLab