diff options
| author | Christoph Hellwig <hch@lst.de> | 2017-01-20 09:31:54 -0800 |
|---|---|---|
| committer | Darrick J. Wong <darrick.wong@oracle.com> | 2017-01-23 10:55:07 -0800 |
| commit | d2b3964a0780d2d2994eba57f950d6c9fe489ed8 (patch) | |
| tree | e5431a683b41059abd0032aa46685ae78d766a50 /fs/xfs/libxfs/xfs_bmap.h | |
| parent | 7a308bb3016f57e5be11a677d15b821536419d36 (diff) | |
| download | lwn-d2b3964a0780d2d2994eba57f950d6c9fe489ed8.tar.gz lwn-d2b3964a0780d2d2994eba57f950d6c9fe489ed8.zip | |
xfs: fix COW writeback race
Due to the way how xfs_iomap_write_allocate tries to convert the whole
found extents from delalloc to real space we can run into a race
condition with multiple threads doing writes to this same extent.
For the non-COW case that is harmless as the only thing that can happen
is that we call xfs_bmapi_write on an extent that has already been
converted to a real allocation. For COW writes where we move the extent
from the COW to the data fork after I/O completion the race is, however,
not quite as harmless. In the worst case we are now calling
xfs_bmapi_write on a region that contains hole in the COW work, which
will trip up an assert in debug builds or lead to file system corruption
in non-debug builds. This seems to be reproducible with workloads of
small O_DSYNC write, although so far I've not managed to come up with
a with an isolated reproducer.
The fix for the issue is relatively simple: tell xfs_bmapi_write
that we are only asked to convert delayed allocations and skip holes
in that case.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Diffstat (limited to 'fs/xfs/libxfs/xfs_bmap.h')
| -rw-r--r-- | fs/xfs/libxfs/xfs_bmap.h | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h index cecd094404cc..cdef87db5262 100644 --- a/fs/xfs/libxfs/xfs_bmap.h +++ b/fs/xfs/libxfs/xfs_bmap.h @@ -110,6 +110,9 @@ struct xfs_extent_free_item /* Map something in the CoW fork. */ #define XFS_BMAPI_COWFORK 0x200 +/* Only convert delalloc space, don't allocate entirely new extents */ +#define XFS_BMAPI_DELALLOC 0x400 + #define XFS_BMAPI_FLAGS \ { XFS_BMAPI_ENTIRE, "ENTIRE" }, \ { XFS_BMAPI_METADATA, "METADATA" }, \ @@ -120,7 +123,8 @@ struct xfs_extent_free_item { XFS_BMAPI_CONVERT, "CONVERT" }, \ { XFS_BMAPI_ZERO, "ZERO" }, \ { XFS_BMAPI_REMAP, "REMAP" }, \ - { XFS_BMAPI_COWFORK, "COWFORK" } + { XFS_BMAPI_COWFORK, "COWFORK" }, \ + { XFS_BMAPI_DELALLOC, "DELALLOC" } static inline int xfs_bmapi_aflag(int w) |