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Subject[PATCH 4.11 107/115] xfs: reserve enough blocks to handle btree splits when remapping
Date
4.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Darrick J. Wong <darrick.wong@oracle.com>

commit fe0be23e68200573de027de9b8cc2b27e7fce35e upstream.

In xfs_reflink_end_cow, we erroneously reserve only enough blocks to
handle adding 1 extent. This is problematic if we fragment free space,
have to do CoW, and then have to perform multiple bmap btree expansions.
Furthermore, the BUI recovery routine doesn't reserve /any/ blocks to
handle btree splits, so log recovery fails after our first error causes
the filesystem to go down.

Therefore, refactor the transaction block reservation macros until we
have a macro that works for our deferred (re)mapping activities, and fix
both problems by using that macro.

With 1k blocks we can hit this fairly often in g/187 if the scratch fs
is big enough.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/xfs/libxfs/xfs_trans_space.h | 23 +++++++++++++++++------
fs/xfs/xfs_bmap_item.c | 5 ++++-
fs/xfs/xfs_reflink.c | 18 ++++++++++++++++--
3 files changed, 37 insertions(+), 9 deletions(-)

--- a/fs/xfs/libxfs/xfs_trans_space.h
+++ b/fs/xfs/libxfs/xfs_trans_space.h
@@ -21,8 +21,20 @@
/*
* Components of space reservations.
*/
+
+/* Worst case number of rmaps that can be held in a block. */
#define XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp) \
(((mp)->m_rmap_mxr[0]) - ((mp)->m_rmap_mnr[0]))
+
+/* Adding one rmap could split every level up to the top of the tree. */
+#define XFS_RMAPADD_SPACE_RES(mp) ((mp)->m_rmap_maxlevels)
+
+/* Blocks we might need to add "b" rmaps to a tree. */
+#define XFS_NRMAPADD_SPACE_RES(mp, b)\
+ (((b + XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp) - 1) / \
+ XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp)) * \
+ XFS_RMAPADD_SPACE_RES(mp))
+
#define XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp) \
(((mp)->m_alloc_mxr[0]) - ((mp)->m_alloc_mnr[0]))
#define XFS_EXTENTADD_SPACE_RES(mp,w) (XFS_BM_MAXLEVELS(mp,w) - 1)
@@ -30,13 +42,12 @@
(((b + XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp) - 1) / \
XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp)) * \
XFS_EXTENTADD_SPACE_RES(mp,w))
+
+/* Blocks we might need to add "b" mappings & rmappings to a file. */
#define XFS_SWAP_RMAP_SPACE_RES(mp,b,w)\
- (((b + XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp) - 1) / \
- XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp)) * \
- XFS_EXTENTADD_SPACE_RES(mp,w) + \
- ((b + XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp) - 1) / \
- XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp)) * \
- (mp)->m_rmap_maxlevels)
+ (XFS_NEXTENTADD_SPACE_RES((mp), (b), (w)) + \
+ XFS_NRMAPADD_SPACE_RES((mp), (b)))
+
#define XFS_DAENTER_1B(mp,w) \
((w) == XFS_DATA_FORK ? (mp)->m_dir_geo->fsbcount : 1)
#define XFS_DAENTER_DBS(mp,w) \
--- a/fs/xfs/xfs_bmap_item.c
+++ b/fs/xfs/xfs_bmap_item.c
@@ -34,6 +34,8 @@
#include "xfs_bmap.h"
#include "xfs_icache.h"
#include "xfs_trace.h"
+#include "xfs_bmap_btree.h"
+#include "xfs_trans_space.h"


kmem_zone_t *xfs_bui_zone;
@@ -446,7 +448,8 @@ xfs_bui_recover(
return -EIO;
}

- error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0, 0, 0, &tp);
+ error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate,
+ XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK), 0, 0, &tp);
if (error)
return error;
budp = xfs_trans_get_bud(tp, buip);
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -709,8 +709,22 @@ xfs_reflink_end_cow(
offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);

- /* Start a rolling transaction to switch the mappings */
- resblks = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
+ /*
+ * Start a rolling transaction to switch the mappings. We're
+ * unlikely ever to have to remap 16T worth of single-block
+ * extents, so just cap the worst case extent count to 2^32-1.
+ * Stick a warning in just in case, and avoid 64-bit division.
+ */
+ BUILD_BUG_ON(MAX_RW_COUNT > UINT_MAX);
+ if (end_fsb - offset_fsb > UINT_MAX) {
+ error = -EFSCORRUPTED;
+ xfs_force_shutdown(ip->i_mount, SHUTDOWN_CORRUPT_INCORE);
+ ASSERT(0);
+ goto out;
+ }
+ resblks = XFS_NEXTENTADD_SPACE_RES(ip->i_mount,
+ (unsigned int)(end_fsb - offset_fsb),
+ XFS_DATA_FORK);
error = xfs_trans_alloc(ip->i_mount, &M_RES(ip->i_mount)->tr_write,
resblks, 0, 0, &tp);
if (error)

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