This is a note to let you know that I've just added the patch titled
xfs: fix COW writeback race
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xfs-fix-cow-writeback-race.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From hch@xxxxxx Thu Feb 2 11:15:22 2017
From: Christoph Hellwig <hch@xxxxxx>
Date: Thu, 2 Feb 2017 08:56:06 +0100
Subject: xfs: fix COW writeback race
To: stable@xxxxxxxxxxxxxxx
Cc: linux-xfs@xxxxxxxxxxxxxxx, "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Message-ID: <1486022171-8076-15-git-send-email-hch@xxxxxx>
From: Christoph Hellwig <hch@xxxxxx>
commit d2b3964a0780d2d2994eba57f950d6c9fe489ed8 upstream.
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@xxxxxx>
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/xfs/libxfs/xfs_bmap.c | 44 ++++++++++++++++++++++++++++++++------------
fs/xfs/libxfs/xfs_bmap.h | 6 +++++-
fs/xfs/xfs_iomap.c | 2 +-
3 files changed, 38 insertions(+), 14 deletions(-)
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -4607,8 +4607,6 @@ xfs_bmapi_write(
int n; /* current extent index */
xfs_fileoff_t obno; /* old block number (offset) */
int whichfork; /* data or attr fork */
- char inhole; /* current location is hole in file */
- char wasdelay; /* old extent was delayed */
#ifdef DEBUG
xfs_fileoff_t orig_bno; /* original block number value */
@@ -4694,22 +4692,44 @@ xfs_bmapi_write(
bma.firstblock = firstblock;
while (bno < end && n < *nmap) {
- inhole = eof || bma.got.br_startoff > bno;
- wasdelay = !inhole && isnullstartblock(bma.got.br_startblock);
+ bool need_alloc = false, wasdelay = false;
- /*
- * Make sure we only reflink into a hole.
- */
- if (flags & XFS_BMAPI_REMAP)
- ASSERT(inhole);
- if (flags & XFS_BMAPI_COWFORK)
- ASSERT(!inhole);
+ /* in hole or beyoned EOF? */
+ if (eof || bma.got.br_startoff > bno) {
+ if (flags & XFS_BMAPI_DELALLOC) {
+ /*
+ * For the COW fork we can reasonably get a
+ * request for converting an extent that races
+ * with other threads already having converted
+ * part of it, as there converting COW to
+ * regular blocks is not protected using the
+ * IOLOCK.
+ */
+ ASSERT(flags & XFS_BMAPI_COWFORK);
+ if (!(flags & XFS_BMAPI_COWFORK)) {
+ error = -EIO;
+ goto error0;
+ }
+
+ if (eof || bno >= end)
+ break;
+ } else {
+ need_alloc = true;
+ }
+ } else {
+ /*
+ * Make sure we only reflink into a hole.
+ */
+ ASSERT(!(flags & XFS_BMAPI_REMAP));
+ if (isnullstartblock(bma.got.br_startblock))
+ wasdelay = true;
+ }
/*
* First, deal with the hole before the allocated space
* that we found, if any.
*/
- if (inhole || wasdelay) {
+ if (need_alloc || wasdelay) {
bma.eof = eof;
bma.conv = !!(flags & XFS_BMAPI_CONVERT);
bma.wasdel = wasdelay;
--- 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)
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -681,7 +681,7 @@ xfs_iomap_write_allocate(
xfs_trans_t *tp;
int nimaps;
int error = 0;
- int flags = 0;
+ int flags = XFS_BMAPI_DELALLOC;
int nres;
if (whichfork == XFS_COW_FORK)
Patches currently in stable-queue which might be from hch@xxxxxx are
queue-4.9/xfs-don-t-rely-on-total-in-xfs_alloc_space_available.patch
queue-4.9/xfs-replace-xfs_mode_to_ftype-table-with-switch-statement.patch
queue-4.9/xfs-fix-bogus-minleft-manipulations.patch
queue-4.9/xfs-fix-cow-writeback-race.patch
queue-4.9/xfs-sanity-check-inode-mode-when-creating-new-dentry.patch
queue-4.9/xfs-extsize-hints-are-not-unlikely-in-xfs_bmap_btalloc.patch
queue-4.9/xfs-bump-up-reserved-blocks-in-xfs_alloc_set_aside.patch
queue-4.9/xfs-add-missing-include-dependencies-to-xfs_dir2.h.patch
queue-4.9/xfs-fix-bmv_count-confusion-w-shared-extents.patch
queue-4.9/xfs-adjust-allocation-length-in-xfs_alloc_space_available.patch
queue-4.9/xfs-verify-dirblocklog-correctly.patch
queue-4.9/xfs-fix-xfs_mode_to_ftype-prototype.patch
queue-4.9/xfs-clear-_xbf_pages-from-buffers-when-readahead-page.patch
queue-4.9/xfs-remove-racy-hasattr-check-from-attr-ops.patch
queue-4.9/xfs-make-the-assert-condition-likely.patch
queue-4.9/xfs-sanity-check-directory-inode-di_size.patch
queue-4.9/xfs-don-t-print-warnings-when-xfs_log_force-fails.patch
queue-4.9/xfs-don-t-wrap-id-in-xfs_dq_get_next_id.patch
queue-4.9/xfs-sanity-check-inode-di_mode.patch
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html