From: Zizhi Wo wozizhi@huawei.com

hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IAC63K CVE: NA

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In the file system expansion test and concurrent file creation and writing scenarios, file creation fails occasionally.

The detailed test scheme is as follows: 1. If the remaining space is less than 128 MB, expand the space by 1 GB; --xfs_growfs /$DEV -D $bc -m 100 2. 32 processes create a file every 0.5s and write 4 KB to 4 MB data randomly. --filesize=$((RANDOM % 1024 + 1)) --dd if=/dev/zero oflag=direct of=$filename bs=4K count=$filesize And when the file creation fails, there are still hundreds of megabytes of free space. The overall analysis process is as follows:

Direct write Create file xfs_file_write_iter ... xfs_direct_write_iomap_begin xfs_iomap_write_direct ... xfs_alloc_vextent xfs_alloc_ag_vextent xfs_alloc_ag_vextent_near xfs_alloc_cur_finish xfs_alloc_fixup_trees xfs_btree_delete xfs_btree_delrec xfs_allocbt_update_lastrec /* The longest update is 0 * because numrec == 0. */ agf->agf_longest = len = 0 xfs_create ... xfs_dialloc xfs_ialloc_ag_alloc xfs_alloc_vextent xfs_alloc_fix_freelist xfs_alloc_space_available -> as longest=0, it will return false, no space for inode alloc.

The root cause of the problem is that allocation extents holds agf locks, but the inode creation process will quickly check whether there is space firstly, which does not have agf locks. And when the first judgment fails, it returns directly. If the first judgment passes, the lock is held before entering the second judgment, that's how the "check-lock-check again" algorithm is designed. If all AG fails in no lock check, an error will return. This problem occurs probably when there is not enough space left for all the AG's in front, and the last AG deletes the last CNT tree record and the new record is not inserted yet.

Fix this issue by adding the bc_free_longest field to the xfs_btree_cur_t structure to store the longest count that will be updated. The assignment is done in xfs_alloc_fixup_trees() and xfs_free_ag_extent().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Zizhi Wo wozizhi@huawei.com Signed-off-by: Long Li leo.lilong@huawei.com --- fs/xfs/libxfs/xfs_alloc.c | 14 ++++++++++++++ fs/xfs/libxfs/xfs_alloc_btree.c | 9 ++++++++- fs/xfs/libxfs/xfs_btree.h | 1 + 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c index b901eedf3bb8..95bfe89651ad 100644 --- a/fs/xfs/libxfs/xfs_alloc.c +++ b/fs/xfs/libxfs/xfs_alloc.c @@ -543,6 +543,13 @@ xfs_alloc_fixup_trees( nfbno2 = rbno + rlen; nflen2 = (fbno + flen) - nfbno2; } + + /* + * Record the potential maximum free length in advance. + */ + if (nfbno1 != NULLAGBLOCK || nfbno2 != NULLAGBLOCK) + cnt_cur->bc_free_longest = max_t(xfs_extlen_t, nflen1, nflen2); + /* * Delete the entry from the by-size btree. */ @@ -2039,6 +2046,13 @@ xfs_free_ag_extent( * Now allocate and initialize a cursor for the by-size tree. */ cnt_cur = xfs_allocbt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_CNT); + /* + * Record the potential maximum free length in advance. + */ + if (haveleft) + cnt_cur->bc_free_longest = ltlen; + if (haveright) + cnt_cur->bc_free_longest = gtlen; /* * Have both left and right contiguous neighbors. * Merge all three into a single free block. diff --git a/fs/xfs/libxfs/xfs_alloc_btree.c b/fs/xfs/libxfs/xfs_alloc_btree.c index 613a1743fdd5..d6dbbe85e819 100644 --- a/fs/xfs/libxfs/xfs_alloc_btree.c +++ b/fs/xfs/libxfs/xfs_alloc_btree.c @@ -147,7 +147,14 @@ xfs_allocbt_update_lastrec( rrp = XFS_ALLOC_REC_ADDR(cur->bc_mp, block, numrecs); len = rrp->ar_blockcount; } else { - len = 0; + /* + * Update in advance to prevent file creation failure + * for concurrent processes even though there is no + * numrec currently. + * And there's no need to worry as the value that not + * less than bc_free_longest will be inserted later. + */ + len = cpu_to_be32(cur->bc_free_longest); }

break; diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h index d172046ae833..1d89b897c056 100644 --- a/fs/xfs/libxfs/xfs_btree.h +++ b/fs/xfs/libxfs/xfs_btree.h @@ -235,6 +235,7 @@ typedef struct xfs_btree_cur struct xfs_btree_cur_ag bc_ag; struct xfs_btree_cur_ino bc_ino; }; + xfs_extlen_t bc_free_longest; /* the actual longest free extent */ } xfs_btree_cur_t;

/* cursor flags */