From: Brian Foster bfoster@redhat.com
mainline-inclusion from mainline-v5.11-rc4 commit b0eb9e1182668b0e9cf81dbf38041cfb8c12887f category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I4KIAO CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Now that log covering occurs on quiesce, we'd like to reuse the underlying superblock sync for final superblock updates. This includes things like lazy superblock counter updates, log feature incompat bits in the future, etc. One quirk to this approach is that once the log is in the IDLE (i.e. already covered) state, any subsequent log write resets the state back to NEED. This means that a final superblock sync to an already covered log requires two more sb syncs to return the log back to IDLE again.
For example, if a lazy superblock enabled filesystem is mount cycled without any modifications, the unmount path syncs the superblock once and writes an unmount record. With the desired log quiesce covering behavior, we sync the superblock three times at unmount time: once for the lazy superblock counter update and twice more to cover the log. By contrast, if the log is active or only partially covered at unmount time, a final superblock sync would doubly serve as the one or two remaining syncs required to cover the log.
This duplicate covering sequence is unnecessary because the filesystem remains consistent if a crash occurs at any point. The superblock will either be recovered in the event of a crash or written back before the log is quiesced and potentially cleaned with an unmount record.
Update the log covering state machine to remain in the IDLE state if additional covering checkpoints pass through the log. This facilitates final superblock updates (such as lazy superblock counters) via a single sb sync without losing covered status. This provides some consistency with the active and partially covered cases and also avoids harmless, but spurious checkpoints when quiescing the log.
Signed-off-by: Brian Foster bfoster@redhat.com Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Reviewed-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Darrick J. Wong djwong@kernel.org Reviewed-by: Allison Henderson allison.henderson@oracle.com Signed-off-by: Guo Xuenan guoxuenan@huawei.com Reviewed-by: Lihong Kou koulihong@huawei.com Reviewed-by: Zhang Yi yi.zhang@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- fs/xfs/xfs_log.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c index fa2d05e65ff1..b70b7d041d79 100644 --- a/fs/xfs/xfs_log.c +++ b/fs/xfs/xfs_log.c @@ -2538,12 +2538,15 @@ xlog_covered_state( int iclogs_changed) { /* - * We usually go to NEED. But we go to NEED2 if the changed indicates we - * are done writing the dummy record. If we are done with the second - * dummy recored (DONE2), then we go to IDLE. + * We go to NEED for any non-covering writes. We go to NEED2 if we just + * wrote the first covering record (DONE). We go to IDLE if we just + * wrote the second covering record (DONE2) and remain in IDLE until a + * non-covering write occurs. */ switch (prev_state) { case XLOG_STATE_COVER_IDLE: + if (iclogs_changed == 1) + return XLOG_STATE_COVER_IDLE; case XLOG_STATE_COVER_NEED: case XLOG_STATE_COVER_NEED2: break;