On a higly fragmented filesystem a Direct IO write can fail with -ENOSPC error
even though the filesystem has sufficient number of free blocks.
This occurs if the file offset range on which the write operation is being
performed has a delalloc extent in the cow fork and this delalloc extent
begins much before the Direct IO range.
In such a scenario, xfs_reflink_allocate_cow() invokes xfs_bmapi_write() to
allocate the blocks mapped by the delalloc extent. The extent thus allocated
may not cover the beginning of file offset range on which the Direct IO write
was issued. Hence xfs_reflink_allocate_cow() ends up returning -ENOSPC.
The following script reliably recreates the bug described above.
#!/usr/bin/bash
device=/dev/loop0
shortdev=$(basename $device)
mntpnt=/mnt/
file1=${mntpnt}/file1
file2=${mntpnt}/file2
fragmentedfile=${mntpnt}/fragmentedfile
punchprog=/root/repos/xfstests-dev/src/punch-alternating
errortag=/sys/fs/xfs/${shortdev}/errortag/bmap_alloc_minlen_extent
umount $device > /dev/null 2>&1
echo "Create FS"
mkfs.xfs -f -m reflink=1 $device > /dev/null 2>&1
if [[ $? != 0 ]]; then
echo "mkfs failed."
exit 1
fi
echo "Mount FS"
mount $device $mntpnt > /dev/null 2>&1
if [[ $? != 0 ]]; then
echo "mount failed."
exit 1
fi
echo "Create source file"
xfs_io -f -c "pwrite 0 32M" $file1 > /dev/null 2>&1
sync
echo "Create Reflinked file"
xfs_io -f -c "reflink $file1" $file2 &>/dev/null
echo "Set cowextsize"
xfs_io -c "cowextsize 16M" $file1 > /dev/null 2>&1
echo "Fragment FS"
xfs_io -f -c "pwrite 0 64M" $fragmentedfile > /dev/null 2>&1
sync
$punchprog $fragmentedfile
echo "Allocate block sized extent from now onwards"
echo -n 1 > $errortag
echo "Create 16MiB delalloc extent in CoW fork"
xfs_io -c "pwrite 0 4k" $file1 > /dev/null 2>&1
sync
echo "Direct I/O write at offset 12k"
xfs_io -d -c "pwrite 12k 8k" $file1
This commit fixes the bug by invoking xfs_bmapi_write() in a loop until disk
blocks are allocated for atleast the starting file offset of the Direct IO
write range.
Root-caused-by: Wengang Wang <wen.gang.wang@xxxxxxxxxx>
Signed-off-by: Chandan Babu R <chandan.babu@xxxxxxxxxx>
---
fs/xfs/xfs_reflink.c | 225 +++++++++++++++++++++++++++++++++++--------
1 file changed, 187 insertions(+), 38 deletions(-)
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index e7a7c00d93be..ab7a39244920 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -340,9 +340,41 @@ xfs_find_trim_cow_extent(
return 0;
}
-/* Allocate all CoW reservations covering a range of blocks in a file. */
-int
-xfs_reflink_allocate_cow(
+static int
+xfs_reflink_convert_unwritten(
+ struct xfs_inode *ip,
+ struct xfs_bmbt_irec *imap,
+ struct xfs_bmbt_irec *cmap,
+ bool convert_now)
+{
+ xfs_fileoff_t offset_fsb = imap->br_startoff;
+ xfs_filblks_t count_fsb = imap->br_blockcount;
+ int error;
+
+ /*
+ * cmap might larger than imap due to cowextsize hint.
+ */
+ xfs_trim_extent(cmap, offset_fsb, count_fsb);
+
+ /*
+ * COW fork extents are supposed to remain unwritten until we're ready
+ * to initiate a disk write. For direct I/O we are going to write the
+ * data and need the conversion, but for buffered writes we're done.
+ */
+ if (!convert_now || cmap->br_state == XFS_EXT_NORM)
+ return 0;
+
+ trace_xfs_reflink_convert_cow(ip, cmap);
+
+ error = xfs_reflink_convert_cow_locked(ip, offset_fsb, count_fsb);
+ if (!error)
+ cmap->br_state = XFS_EXT_NORM;
+
+ return error;
+}
+
+static int
+xfs_reflink_alloc_cow_unwritten(
struct xfs_inode *ip,
struct xfs_bmbt_irec *imap,
struct xfs_bmbt_irec *cmap,
@@ -351,33 +383,17 @@ xfs_reflink_allocate_cow(
bool convert_now)
{
struct xfs_mount *mp = ip->i_mount;
- xfs_fileoff_t offset_fsb = imap->br_startoff;
- xfs_filblks_t count_fsb = imap->br_blockcount;
struct xfs_trans *tp;
- int nimaps, error = 0;
- bool found;
xfs_filblks_t resaligned;
- xfs_extlen_t resblks = 0;
-
- ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
- if (!ip->i_cowfp) {
- ASSERT(!xfs_is_reflink_inode(ip));
- xfs_ifork_init_cow(ip);
- }
-
- error = xfs_find_trim_cow_extent(ip, imap, cmap, shared, &found);
- if (error || !*shared)
- return error;
- if (found)
- goto convert;
+ xfs_extlen_t resblks;
+ int nimaps;
+ int error;
+ bool found;
resaligned = xfs_aligned_fsb_count(imap->br_startoff,
imap->br_blockcount, xfs_get_cowextsz_hint(ip));
resblks = XFS_DIOSTRAT_SPACE_RES(mp, resaligned);
- xfs_iunlock(ip, *lockmode);
- *lockmode = 0;
-
error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_write, resblks, 0,
false, &tp);
if (error)
@@ -385,17 +401,17 @@ xfs_reflink_allocate_cow(
*lockmode = XFS_ILOCK_EXCL;
- /*
- * Check for an overlapping extent again now that we dropped the ilock.
- */
error = xfs_find_trim_cow_extent(ip, imap, cmap, shared, &found);
if (error || !*shared)
goto out_trans_cancel;
+
if (found) {
xfs_trans_cancel(tp);
goto convert;
}
+ ASSERT(cmap->br_startoff > imap->br_startoff);
+
/* Allocate the entire reservation as unwritten blocks. */
nimaps = 1;
error = xfs_bmapi_write(tp, ip, imap->br_startoff, imap->br_blockcount,
@@ -415,19 +431,9 @@ xfs_reflink_allocate_cow(
*/
if (nimaps == 0)
return -ENOSPC;
+
convert:
- xfs_trim_extent(cmap, offset_fsb, count_fsb);
- /*
- * COW fork extents are supposed to remain unwritten until we're ready
- * to initiate a disk write. For direct I/O we are going to write the
- * data and need the conversion, but for buffered writes we're done.
- */
- if (!convert_now || cmap->br_state == XFS_EXT_NORM)
- return 0;
- trace_xfs_reflink_convert_cow(ip, cmap);
- error = xfs_reflink_convert_cow_locked(ip, offset_fsb, count_fsb);
- if (!error)
- cmap->br_state = XFS_EXT_NORM;
+ error = xfs_reflink_convert_unwritten(ip, imap, cmap, convert_now);
return error;
out_trans_cancel:
@@ -435,6 +441,149 @@ xfs_reflink_allocate_cow(
return error;
}
+static int
+xfs_replace_delalloc_cow_extent(
+ struct xfs_inode *ip,
+ struct xfs_bmbt_irec *imap,
+ struct xfs_bmbt_irec *cmap,
+ bool *shared,
+ uint *lockmode,
+ bool convert_now)
+{
+ struct xfs_mount *mp = ip->i_mount;
+ struct xfs_trans *tp;
+ int nimaps;
+ int error;
+ bool found;
+
+ while (1) {
+ error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_write, 0, 0,
+ false, &tp);
+ if (error)
+ return error;
+
+ *lockmode = XFS_ILOCK_EXCL;
+
+ error = xfs_find_trim_cow_extent(ip, imap, cmap, shared,
+ &found);
+ if (error || !*shared)
+ goto out_trans_cancel;
+
+ if (found) {
+ xfs_trans_cancel(tp);
+ goto convert;
+ }
+
+ ASSERT(isnullstartblock(cmap->br_startblock) ||
+ cmap->br_startblock == DELAYSTARTBLOCK);
+
+ /*
+ * Replace delalloc reservation with an unwritten extent.
+ */
+ nimaps = 1;
+ error = xfs_bmapi_write(tp, ip, cmap->br_startoff,
+ cmap->br_blockcount,
+ XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC, 0, cmap,
+ &nimaps);
+ if (error)
+ goto out_trans_cancel;
+
+ xfs_inode_set_cowblocks_tag(ip);
+ error = xfs_trans_commit(tp);
+ if (error)
+ return error;
+
+ /*
+ * Allocation succeeded but the requested range was not even partially
+ * satisfied? Bail out!
+ */
+ if (nimaps == 0)
+ return -ENOSPC;
+
+ if (cmap->br_startoff + cmap->br_blockcount > imap->br_startoff)
+ break;
+
+ xfs_iunlock(ip, *lockmode);
+ *lockmode = 0;
+ }
+
+convert:
+ error = xfs_reflink_convert_unwritten(ip, imap, cmap, convert_now);
+ return error;
+
+out_trans_cancel:
+ xfs_trans_cancel(tp);
+ return error;
+}
+
+
+/* Allocate all CoW reservations covering a range of blocks in a file. */
+int
+xfs_reflink_allocate_cow(
+ struct xfs_inode *ip,
+ struct xfs_bmbt_irec *imap,
+ struct xfs_bmbt_irec *cmap,
+ bool *shared,
+ uint *lockmode,
+ bool convert_now)
+{
+ int error;
+ bool found;
+
+ ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
+ if (!ip->i_cowfp) {
+ ASSERT(!xfs_is_reflink_inode(ip));
+ xfs_ifork_init_cow(ip);
+ }
+
+ error = xfs_find_trim_cow_extent(ip, imap, cmap, shared, &found);
+ if (error || !*shared)
+ return error;
+
+ /*
+ * We have to deal with one of the following 2 cases,
+ * 1. No extent in CoW fork and shared extent in Data fork.
+ * 2. CoW fork has one of the following:
+ * - Unwritten/written extent in CoW fork.
+ * - Delalloc extent in CoW fork; An extent may or may not be present
+ * in the Data fork.
+ */
+
+ if (found) {
+ /*
+ * CoW fork has a real extent; Convert it to written if is an
+ * unwritten extent.
+ */
+ error = xfs_reflink_convert_unwritten(ip, imap, cmap,
+ convert_now);
+ return error;
+ }
+
+ xfs_iunlock(ip, *lockmode);
+ *lockmode = 0;
+
+ if (cmap->br_startoff > imap->br_startoff) {
+ /*
+ * CoW fork does not have an extent. Hence, allocate a real
+ * extent in the CoW fork.
+ */
+ error = xfs_reflink_alloc_cow_unwritten(ip, imap, cmap, shared,
+ lockmode, convert_now);
+ } else if (isnullstartblock(cmap->br_startblock) ||
+ cmap->br_startblock == DELAYSTARTBLOCK) {
+ /*
+ * CoW fork has a delalloc extent. Replace it with a real
+ * extent.
+ */
+ error = xfs_replace_delalloc_cow_extent(ip, imap, cmap, shared,
+ lockmode, convert_now);
+ } else {
+ ASSERT(0);
+ }
+
+ return error;
+}
+
/*
* Cancel CoW reservations for some block range of an inode.
*
--
2.35.1
