On 3/31/21 6:09 PM, Darrick J. Wong wrote:
From: Darrick J. Wong <djwong@xxxxxxxxxx>
When there are no ongoing transactions and the log contents have been
checkpointed back into the filesystem, the log performs 'covering',
which is to say that it log a dummy transaction to record the fact that
the tail has caught up with the head. This is a good time to clear log
incompat feature flags, because they are flags that are temporarily set
to limit the range of kernels that can replay a dirty log.
Since it's possible that some other higher level thread is about to
start logging items protected by a log incompat flag, we create a rwsem
so that upper level threads can coordinate this with the log. It would
probably be more performant to use a percpu rwsem, but the ability to
/try/ taking the write lock during covering is critical, and percpu
rwsems do not provide that.
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
ok, makes sense
Reviewed-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
---
fs/xfs/libxfs/xfs_shared.h | 6 +++++
fs/xfs/xfs_log.c | 49 ++++++++++++++++++++++++++++++++++++++++++++
fs/xfs/xfs_log.h | 3 +++
fs/xfs/xfs_log_priv.h | 3 +++
fs/xfs/xfs_trans.c | 14 +++++++++----
5 files changed, 71 insertions(+), 4 deletions(-)
diff --git a/fs/xfs/libxfs/xfs_shared.h b/fs/xfs/libxfs/xfs_shared.h
index 8c61a461bf7b..c7c9a0cebb04 100644
--- a/fs/xfs/libxfs/xfs_shared.h
+++ b/fs/xfs/libxfs/xfs_shared.h
@@ -62,6 +62,12 @@ void xfs_log_get_max_trans_res(struct xfs_mount *mp,
#define XFS_TRANS_SB_DIRTY 0x02 /* superblock is modified */
#define XFS_TRANS_PERM_LOG_RES 0x04 /* xact took a permanent log res */
#define XFS_TRANS_SYNC 0x08 /* make commit synchronous */
+/*
+ * This transaction uses a log incompat feature, which means that we must tell
+ * the log that we've finished using it at the transaction commit or cancel.
+ * Callers must call xlog_use_incompat_feat before setting this flag.
+ */
+#define XFS_TRANS_LOG_INCOMPAT 0x10
#define XFS_TRANS_RESERVE 0x20 /* OK to use reserved data blocks */
#define XFS_TRANS_NO_WRITECOUNT 0x40 /* do not elevate SB writecount */
#define XFS_TRANS_RES_FDBLKS 0x80 /* reserve newly freed blocks */
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index cf73bc9f4d18..cb72be62da3e 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -1335,6 +1335,32 @@ xfs_log_work_queue(
msecs_to_jiffies(xfs_syncd_centisecs * 10));
}
+/*
+ * Clear the log incompat flags if we have the opportunity.
+ *
+ * This only happens if we're about to log the second dummy transaction as part
+ * of covering the log and we can get the log incompat feature usage lock.
+ */
+static inline void
+xlog_clear_incompat(
+ struct xlog *log)
+{
+ struct xfs_mount *mp = log->l_mp;
+
+ if (!xfs_sb_has_incompat_log_feature(&mp->m_sb,
+ XFS_SB_FEAT_INCOMPAT_LOG_ALL))
+ return;
+
+ if (log->l_covered_state != XLOG_STATE_COVER_DONE2)
+ return;
+
+ if (!down_write_trylock(&log->l_incompat_users))
+ return;
+
+ xfs_clear_incompat_log_features(mp);
+ up_write(&log->l_incompat_users);
+}
+
/*
* Every sync period we need to unpin all items in the AIL and push them to
* disk. If there is nothing dirty, then we might need to cover the log to
@@ -1361,6 +1387,7 @@ xfs_log_worker(
* synchronously log the superblock instead to ensure the
* superblock is immediately unpinned and can be written back.
*/
+ xlog_clear_incompat(log);
xfs_sync_sb(mp, true);
} else
xfs_log_force(mp, 0);
@@ -1443,6 +1470,8 @@ xlog_alloc_log(
}
log->l_sectBBsize = 1 << log2_size;
+ init_rwsem(&log->l_incompat_users);
+
xlog_get_iclog_buffer_size(mp, log);
spin_lock_init(&log->l_icloglock);
@@ -3933,3 +3962,23 @@ xfs_log_in_recovery(
return log->l_flags & XLOG_ACTIVE_RECOVERY;
}
+
+/*
+ * Notify the log that we're about to start using a feature that is protected
+ * by a log incompat feature flag. This will prevent log covering from
+ * clearing those flags.
+ */
+void
+xlog_use_incompat_feat(
+ struct xlog *log)
+{
+ down_read(&log->l_incompat_users);
+}
+
+/* Notify the log that we've finished using log incompat features. */
+void
+xlog_drop_incompat_feat(
+ struct xlog *log)
+{
+ up_read(&log->l_incompat_users);
+}
diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
index 044e02cb8921..8b7d0a56cbf1 100644
--- a/fs/xfs/xfs_log.h
+++ b/fs/xfs/xfs_log.h
@@ -145,4 +145,7 @@ bool xfs_log_in_recovery(struct xfs_mount *);
xfs_lsn_t xlog_grant_push_threshold(struct xlog *log, int need_bytes);
+void xlog_use_incompat_feat(struct xlog *log);
+void xlog_drop_incompat_feat(struct xlog *log);
+
#endif /* __XFS_LOG_H__ */
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 1c6fdbf3d506..75702c4fa69c 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -436,6 +436,9 @@ struct xlog {
#endif
/* log recovery lsn tracking (for buffer submission */
xfs_lsn_t l_recovery_lsn;
+
+ /* Users of log incompat features should take a read lock. */
+ struct rw_semaphore l_incompat_users;
};
#define XLOG_BUF_CANCEL_BUCKET(log, blkno) \
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index eb2d8e2e5db6..e548d53c2091 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -71,6 +71,9 @@ xfs_trans_free(
xfs_extent_busy_sort(&tp->t_busy);
xfs_extent_busy_clear(tp->t_mountp, &tp->t_busy, false);
+ if (tp->t_flags & XFS_TRANS_LOG_INCOMPAT)
+ xlog_drop_incompat_feat(tp->t_mountp->m_log);
+
trace_xfs_trans_free(tp, _RET_IP_);
xfs_trans_clear_context(tp);
if (!(tp->t_flags & XFS_TRANS_NO_WRITECOUNT))
@@ -110,10 +113,13 @@ xfs_trans_dup(
ASSERT(tp->t_flags & XFS_TRANS_PERM_LOG_RES);
ASSERT(tp->t_ticket != NULL);
- ntp->t_flags = XFS_TRANS_PERM_LOG_RES |
- (tp->t_flags & XFS_TRANS_RESERVE) |
- (tp->t_flags & XFS_TRANS_NO_WRITECOUNT) |
- (tp->t_flags & XFS_TRANS_RES_FDBLKS);
+ ntp->t_flags = tp->t_flags & (XFS_TRANS_PERM_LOG_RES |
+ XFS_TRANS_RESERVE |
+ XFS_TRANS_NO_WRITECOUNT |
+ XFS_TRANS_RES_FDBLKS |
+ XFS_TRANS_LOG_INCOMPAT);
+ /* Give our LOG_INCOMPAT reference to the new transaction. */
+ tp->t_flags &= ~XFS_TRANS_LOG_INCOMPAT;
/* We gave our writer reference to the new transaction */
tp->t_flags |= XFS_TRANS_NO_WRITECOUNT;
ntp->t_ticket = xfs_log_ticket_get(tp->t_ticket);
