[PATCH 1/6] xfs: btree format inode forks can have zero extents

Dave Chinner
2021-05-27T04:52:11Z

From: Dave Chinner <dchinner@redhat.com>

xfs/538 is assert failing with this trace when testing with
directory block sizes of 64kB:

XFS: Assertion failed: !xfs_need_iread_extents(ifp), file: fs/xfs/libxfs/xfs_bmap.c, line: 608
....
Call Trace:
xfs_bmap_btree_to_extents+0x2a9/0x470
? kmem_cache_alloc+0xe7/0x220
__xfs_bunmapi+0x4ca/0xdf0
xfs_bunmapi+0x1a/0x30
xfs_dir2_shrink_inode+0x71/0x210
xfs_dir2_block_to_sf+0x2ae/0x410
xfs_dir2_block_removename+0x21a/0x280
xfs_dir_removename+0x195/0x1d0
xfs_remove+0x244/0x460
xfs_vn_unlink+0x53/0xa0
? selinux_inode_unlink+0x13/0x20
vfs_unlink+0x117/0x220
do_unlinkat+0x1a2/0x2d0
__x64_sys_unlink+0x42/0x60
do_syscall_64+0x3a/0x70
entry_SYSCALL_64_after_hwframe+0x44/0xae

This is a check to ensure that the extents have been read into
memory before we are doing a ifork btree manipulation. This assert
is bogus in the above case.

We have a fragmented directory block that has more extents in it
than can fit in extent format, so the inode data fork is in btree
format. xfs_dir2_shrink_inode() asks to remove all remaining 16
filesystem blocks from the inode so it can convert to short form,
and __xfs_bunmapi() removes all the extents. We now have a data fork
in btree format but have zero extents in the fork. This incorrectly
trips the xfs_need_iread_extents() assert because it assumes that an
empty extent btree means the extent tree has not been read into
memory yet. This is clearly not the case with xfs_bunmapi(), as it
has an explicit call to xfs_iread_extents() in it to pull the
extents into memory before it starts unmapping.

Also, the assert directly after this bogus one is:

ASSERT(ifp->if_format == XFS_DINODE_FMT_BTREE);

Which covers the context in which it is legal to call
xfs_bmap_btree_to_extents just fine. Hence we should just remove the
bogus assert as it is clearly wrong and causes a regression.

The returns the test behaviour to the pre-existing assert failure in
xfs_dir2_shrink_inode() that indicates xfs_bunmapi() has failed to
remove all the extents in the range it was asked to unmap.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/libxfs/xfs_bmap.c | 1 -
1 file changed, 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 7e3b9b01431e..3f8b6da09261 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -605,7 +605,6 @@ xfs_bmap_btree_to_extents(

ASSERT(cur);
ASSERT(whichfork != XFS_COW_FORK);
- ASSERT(!xfs_need_iread_extents(ifp));
ASSERT(ifp->if_format == XFS_DINODE_FMT_BTREE);
ASSERT(be16_to_cpu(rblock->bb_level) == 1);
ASSERT(be16_to_cpu(rblock->bb_numrecs) == 1);
--
2.31.1