[PATCH] xfs: make tr_growdata a permanent transaction

Brian Foster
2019-04-17T09:36:10Z

The growdata transaction is used by growfs operations to increase
the data size of the filesystem. Part of this sequence involves
extending the size of the last preexisting AG in the fs, if
necessary. This is implemented by freeing the newly available
physical range to the AG.

tr_growdata is not a permanent transaction, however, and block
allocation transactions must be permanent to handle deferred frees
of AGFL blocks. If the grow operation extends an existing AG that
requires AGFL fixing, assert failures occur due to a populated dfops
list on a non-permanent transaction and the AGFL free does not
occur. This is reproduced (rarely) by xfs/104.

Change tr_growdata to a permanent transaction with a default log
count. This increases initial transaction reservation size, but
growfs is an infrequent and non-performance critical operation and
so should have minimal impact. Also add an assert in the block
allocation path to make this transaction requirement explicit and
obvious to future callers.

Reported-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Brian Foster <bfoster@redhat.com>
---

This is motivated by Darrick's recent xfs/104 failure report[1]. Note
that I made the assert a bit more explicit than originally suggested
because I think any transaction that performs block allocation should be
expected to be able to handle arbitrary AGFL fixups. This survives an
fstests auto run without any regressions[2] or assert failures.

Brian

[1] https://marc.info/?l=linux-xfs&m=155537961822223&w=2
[2] Note that I was never able to reproduce the original xfs/104
failure.

fs/xfs/libxfs/xfs_alloc.c | 2 ++
fs/xfs/libxfs/xfs_trans_resv.c | 6 +++++-
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index bc3367b8b7bb..e4df1866f949 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -2237,6 +2237,8 @@ xfs_alloc_fix_freelist(
xfs_extlen_t need; /* total blocks needed in freelist */
int error = 0;

+ ASSERT(tp->t_flags & XFS_TRANS_PERM_LOG_RES);
+
if (!pag->pagf_init) {
error = xfs_alloc_read_agf(mp, tp, args->agno, flags, &agbp);
if (error)
diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
index f99a7aefe418..83f4ee2afc49 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.c
+++ b/fs/xfs/libxfs/xfs_trans_resv.c
@@ -876,9 +876,13 @@ xfs_trans_resv_calc(
resp->tr_sb.tr_logres = xfs_calc_sb_reservation(mp);
resp->tr_sb.tr_logcount = XFS_DEFAULT_LOG_COUNT;

+ /* growdata requires permanent res; it can free space to the last AG */
+ resp->tr_growdata.tr_logres = xfs_calc_growdata_reservation(mp);
+ resp->tr_growdata.tr_logcount = XFS_DEFAULT_PERM_LOG_COUNT;
+ resp->tr_growdata.tr_logflags |= XFS_TRANS_PERM_LOG_RES;
+
/* The following transaction are logged in logical format */
resp->tr_ichange.tr_logres = xfs_calc_ichange_reservation(mp);
- resp->tr_growdata.tr_logres = xfs_calc_growdata_reservation(mp);
resp->tr_fsyncts.tr_logres = xfs_calc_swrite_reservation(mp);
resp->tr_writeid.tr_logres = xfs_calc_writeid_reservation(mp);
resp->tr_attrsetrt.tr_logres = xfs_calc_attrsetrt_reservation(mp);
--
2.17.2