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[PATCH] xfs: inode log reservations are too small

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: inode log reservations are too small
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 28 Aug 2013 16:10:35 +1000
Delivered-to: xfs@xxxxxxxxxxx
From: Dave Chinner <dchinner@xxxxxxxxxx>

We've been seeing occasional problems with log space leaks and
transaction underruns such as this for some time:

 XFS (dm-0): xlog_write: reservation summary:
   trans type  = FSYNC_TS (36)
   unit res    = 2740 bytes
   current res = -4 bytes
   total reg   = 0 bytes (o/flow = 0 bytes)
   ophdrs      = 0 (ophdr space = 0 bytes)
   ophdr + reg = 0 bytes
   num regions = 0

Turns out that xfstests generic/311 is reliably reproducing this
problem with the test it runs at sequence 16 of it execution. It is
a 100% reliable reproducer with the mkfs configuration of "-b
size=1024 -m crc=1" on a 10GB scratch device.

The problem? Inode forks in btree format are logged in memory
format, not disk format (i.e. bmbt format, not bmdr format). That
means there is a btree block header being logged, when such a
structure is never written to the inode fork in bmdr format. The
bmdr header in the inode is only 4 bytes, while the bmbt header is
24 bytes for v4 filesystems and 72 bytes for v5 filesystems.

We currently reserve the inode size plus the rounded up overhead of
a logging a buffer, which is 128 bytes. That means the reservation
for a 512 byte inode is 640 bytes. What we can actually log is:

        inode core, data and attr fork = 512 bytes
        inode log format + log op header = 56 + 12 = 68 bytes
        data fork bmbt hdr = 24/72 bytes
        attr fork bmbt hdr = 24/72 bytes

So, for a v2 inodes we can log at least 628 bytes, but if we split that
inode over the end of the log across log buffers, we need to also
another log op header, which takes us to 640 bytes. If there's
another reservation taken out of this that I haven't taken into
account (perhaps multiple iclog splits?) or I haven't corectly
calculated the bmbt format space used (entirely possible), then
we will overun it.

For v3 inodes the maximum is actually 724 bytes, and even a
single maximally sized btree format fork can blow it (652 bytes).
And that's exactly what is happening with the FSYNC_TS transaction
in the above output - it's consumed 644 bytes of space after the CIL
context took the space reserved for it (2100 bytes).

This problem has always been present in the XFS code - the btree
format inode forks have always been logged in this manner. Hence
there has always been the possibility of an overrun with such a
transaction. The CRC code has just exposed it frequently enough to
be able to debug and understand the root cause....

So, let's fix all the inode log space reservations.

[ I'm so glad we spent the effort to clean up the transaction
  reservation code. This is an easy fix now. ]

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_trans_resv.c | 72 ++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 53 insertions(+), 19 deletions(-)

diff --git a/fs/xfs/xfs_trans_resv.c b/fs/xfs/xfs_trans_resv.c
index 24110f3..69bcba2 100644
--- a/fs/xfs/xfs_trans_resv.c
+++ b/fs/xfs/xfs_trans_resv.c
@@ -73,6 +73,39 @@ xfs_calc_buf_res(
 }
 
 /*
+ * Logging inodes is really tricksy. They are logged in memory format,
+ * which means that what we write into the log doesn't directory translate into
+ * the amount of space they use on disk.
+ *
+ * Case in point - btree format forks in memory format use more space than the
+ * on-disk format. In memory, the buffer contains a normal btree block header 
so
+ * the btree code can treat it as though it is just another generic buffer.
+ * However, when we write it to the inode fork, we don't write all of this
+ * header as it isn't needed. e.g. the root is only ever in the inode, so
+ * there's no need for sibling pointers which would waste 16 bytes of space.
+ *
+ * Hence when we have an inode with a maximally sized btree format fork, then
+ * amount of information we actually log is greater than the size of the inode
+ * on disk. Hence we need an inode reservation function that calculates all 
this
+ * correctly. So, we log:
+ *
+ * - log op headers for object
+ * - inode log format object
+ * - the entire inode contents (core + 2 forks)
+ * - two bmap btree block headers
+ */
+STATIC uint
+xfs_calc_inode_res(
+       struct xfs_mount        *mp,
+       uint                    ninodes)
+{
+       return ninodes * (sizeof(struct xlog_op_header) +
+                         sizeof(struct xfs_inode_log_format) +
+                         mp->m_sb.sb_inodesize +
+                         2 * XFS_BMBT_BLOCK_LEN(mp));
+}
+
+/*
  * Various log reservation values.
  *
  * These are based on the size of the file system block because that is what
@@ -111,7 +144,7 @@ xfs_calc_write_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               MAX((xfs_calc_buf_res(1, mp->m_sb.sb_inodesize) +
+               MAX((xfs_calc_inode_res(mp, 1) +
                     xfs_calc_buf_res(XFS_BM_MAXLEVELS(mp, XFS_DATA_FORK),
                                      XFS_FSB_TO_B(mp, 1)) +
                     xfs_calc_buf_res(3, mp->m_sb.sb_sectsize) +
@@ -140,7 +173,7 @@ xfs_calc_itruncate_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               MAX((xfs_calc_buf_res(1, mp->m_sb.sb_inodesize) +
+               MAX((xfs_calc_inode_res(mp, 1) +
                     xfs_calc_buf_res(XFS_BM_MAXLEVELS(mp, XFS_DATA_FORK) + 1,
                                      XFS_FSB_TO_B(mp, 1))),
                    (xfs_calc_buf_res(9, mp->m_sb.sb_sectsize) +
@@ -170,7 +203,7 @@ xfs_calc_rename_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               MAX((xfs_calc_buf_res(4, mp->m_sb.sb_inodesize) +
+               MAX((xfs_calc_inode_res(mp, 4) +
                     xfs_calc_buf_res(2 * XFS_DIROP_LOG_COUNT(mp),
                                      XFS_FSB_TO_B(mp, 1))),
                    (xfs_calc_buf_res(7, mp->m_sb.sb_sectsize) +
@@ -195,7 +228,7 @@ xfs_calc_link_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               MAX((xfs_calc_buf_res(2, mp->m_sb.sb_inodesize) +
+               MAX((xfs_calc_inode_res(mp, 2) +
                     xfs_calc_buf_res(XFS_DIROP_LOG_COUNT(mp),
                                      XFS_FSB_TO_B(mp, 1))),
                    (xfs_calc_buf_res(3, mp->m_sb.sb_sectsize) +
@@ -220,7 +253,7 @@ xfs_calc_remove_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               MAX((xfs_calc_buf_res(2, mp->m_sb.sb_inodesize) +
+               MAX((xfs_calc_inode_res(mp, 2) +
                     xfs_calc_buf_res(XFS_DIROP_LOG_COUNT(mp),
                                      XFS_FSB_TO_B(mp, 1))),
                    (xfs_calc_buf_res(5, mp->m_sb.sb_sectsize) +
@@ -247,7 +280,7 @@ STATIC uint
 xfs_calc_create_resv_modify(
        struct xfs_mount        *mp)
 {
-       return xfs_calc_buf_res(2, mp->m_sb.sb_inodesize) +
+       return xfs_calc_inode_res(mp, 2) +
                xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
                (uint)XFS_FSB_TO_B(mp, 1) +
                xfs_calc_buf_res(XFS_DIROP_LOG_COUNT(mp), XFS_FSB_TO_B(mp, 1));
@@ -357,7 +390,7 @@ xfs_calc_ifree_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               xfs_calc_buf_res(1, mp->m_sb.sb_inodesize) +
+               xfs_calc_inode_res(mp, 1) +
                xfs_calc_buf_res(2, mp->m_sb.sb_sectsize) +
                xfs_calc_buf_res(1, XFS_FSB_TO_B(mp, 1)) +
                MAX((__uint16_t)XFS_FSB_TO_B(mp, 1),
@@ -378,9 +411,8 @@ xfs_calc_ichange_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               mp->m_sb.sb_inodesize +
-               mp->m_sb.sb_sectsize +
-               512;
+               xfs_calc_inode_res(mp, 1) +
+               xfs_calc_buf_res(1, mp->m_sb.sb_sectsize);
 
 }
 
@@ -416,7 +448,7 @@ xfs_calc_growrtalloc_reservation(
        return xfs_calc_buf_res(2, mp->m_sb.sb_sectsize) +
                xfs_calc_buf_res(XFS_BM_MAXLEVELS(mp, XFS_DATA_FORK),
                                 XFS_FSB_TO_B(mp, 1)) +
-               xfs_calc_buf_res(1, mp->m_sb.sb_inodesize) +
+               xfs_calc_inode_res(mp, 1) +
                xfs_calc_buf_res(XFS_ALLOCFREE_LOG_COUNT(mp, 1),
                                 XFS_FSB_TO_B(mp, 1));
 }
@@ -448,7 +480,7 @@ xfs_calc_growrtfree_reservation(
        struct xfs_mount        *mp)
 {
        return xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
-               xfs_calc_buf_res(2, mp->m_sb.sb_inodesize) +
+               xfs_calc_inode_res(mp, 2) +
                xfs_calc_buf_res(1, mp->m_sb.sb_blocksize) +
                xfs_calc_buf_res(1, mp->m_rsumsize);
 }
@@ -461,7 +493,7 @@ STATIC uint
 xfs_calc_swrite_reservation(
        struct xfs_mount        *mp)
 {
-       return xfs_calc_buf_res(1, mp->m_sb.sb_inodesize);
+       return xfs_calc_inode_res(mp, 1);
 }
 
 /*
@@ -469,9 +501,10 @@ xfs_calc_swrite_reservation(
  *     inode
  */
 STATIC uint
-xfs_calc_writeid_reservation(xfs_mount_t *mp)
+xfs_calc_writeid_reservation(
+       struct xfs_mount        *mp)
 {
-       return xfs_calc_buf_res(1, mp->m_sb.sb_inodesize);
+       return xfs_calc_inode_res(mp, 1);
 }
 
 /*
@@ -487,7 +520,7 @@ xfs_calc_addafork_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               xfs_calc_buf_res(1, mp->m_sb.sb_inodesize) +
+               xfs_calc_inode_res(mp, 1) +
                xfs_calc_buf_res(2, mp->m_sb.sb_sectsize) +
                xfs_calc_buf_res(1, mp->m_dirblksize) +
                xfs_calc_buf_res(XFS_DAENTER_BMAP1B(mp, XFS_DATA_FORK) + 1,
@@ -511,7 +544,7 @@ STATIC uint
 xfs_calc_attrinval_reservation(
        struct xfs_mount        *mp)
 {
-       return MAX((xfs_calc_buf_res(1, mp->m_sb.sb_inodesize) +
+       return MAX((xfs_calc_inode_res(mp, 1) +
                    xfs_calc_buf_res(XFS_BM_MAXLEVELS(mp, XFS_ATTR_FORK),
                                     XFS_FSB_TO_B(mp, 1))),
                   (xfs_calc_buf_res(9, mp->m_sb.sb_sectsize) +
@@ -535,7 +568,7 @@ xfs_calc_attrsetm_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               xfs_calc_buf_res(1, mp->m_sb.sb_inodesize) +
+               xfs_calc_inode_res(mp, 1) +
                xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
                xfs_calc_buf_res(XFS_DA_NODE_MAXDEPTH, XFS_FSB_TO_B(mp, 1));
 }
@@ -575,7 +608,7 @@ xfs_calc_attrrm_reservation(
        struct xfs_mount        *mp)
 {
        return XFS_DQUOT_LOGRES(mp) +
-               MAX((xfs_calc_buf_res(1, mp->m_sb.sb_inodesize) +
+               MAX((xfs_calc_inode_res(mp, 1) +
                     xfs_calc_buf_res(XFS_DA_NODE_MAXDEPTH,
                                      XFS_FSB_TO_B(mp, 1)) +
                     (uint)XFS_FSB_TO_B(mp,
@@ -627,6 +660,7 @@ STATIC uint
 xfs_calc_qm_dqalloc_reservation(
        struct xfs_mount        *mp)
 {
+       ASSERT(M_RES(mp)->tr_write.tr_logres);
        return M_RES(mp)->tr_write.tr_logres +
                xfs_calc_buf_res(1,
                        XFS_FSB_TO_B(mp, XFS_DQUOT_CLUSTER_SIZE_FSB) - 1);
-- 
1.8.3.2

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