xfs: allow scrubbers to pause background reclaim

The forthcoming summary counter patch races with regular filesystem
activity to compute rough expected values for the counters.  This design
was chosen to avoid having to freeze the entire filesystem to check the
counters, but while that's running we'd prefer to minimize background
reclamation activity to reduce the perturbations to the incore free
block count.  Therefore, provide a way for scrubbers to disable
background posteof and cowblock reclamation.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/scrub/common.c

@@ -894,3 +894,21 @@ xchk_ilock_inverted(
 	}
 	return -EDEADLOCK;
 }
+
+/* Pause background reaping of resources. */
+void
+xchk_stop_reaping(
+	struct xfs_scrub	*sc)
+{
+	sc->flags |= XCHK_REAPING_DISABLED;
+	xfs_stop_block_reaping(sc->mp);
+}
+
+/* Restart background reaping of resources. */
+void
+xchk_start_reaping(
+	struct xfs_scrub	*sc)
+{
+	xfs_start_block_reaping(sc->mp);
+	sc->flags &= ~XCHK_REAPING_DISABLED;
+}

fs/xfs/scrub/common.h

@@ -137,5 +137,7 @@ static inline bool xchk_skip_xref(struct xfs_scrub_metadata *sm)
 
 int xchk_metadata_inode_forks(struct xfs_scrub *sc);
 int xchk_ilock_inverted(struct xfs_inode *ip, uint lock_mode);
+void xchk_stop_reaping(struct xfs_scrub *sc);
+void xchk_start_reaping(struct xfs_scrub *sc);
 
 #endif	/* __XFS_SCRUB_COMMON_H__ */

fs/xfs/scrub/scrub.c

@@ -187,6 +187,8 @@ xchk_teardown(
 			xfs_irele(sc->ip);
 		sc->ip = NULL;
 	}
+	if (sc->flags & XCHK_REAPING_DISABLED)
+		xchk_start_reaping(sc);
 	if (sc->flags & XCHK_HAS_QUOTAOFFLOCK) {
 		mutex_unlock(&sc->mp->m_quotainfo->qi_quotaofflock);
 		sc->flags &= ~XCHK_HAS_QUOTAOFFLOCK;

fs/xfs/scrub/scrub.h

@@ -80,6 +80,7 @@ struct xfs_scrub {
 /* XCHK state flags grow up from zero, XREP state flags grown down from 2^31 */
 #define XCHK_TRY_HARDER		(1 << 0)  /* can't get resources, try again */
 #define XCHK_HAS_QUOTAOFFLOCK	(1 << 1)  /* we hold the quotaoff lock */
+#define XCHK_REAPING_DISABLED	(1 << 2)  /* background block reaping paused */
 #define XREP_ALREADY_FIXED	(1 << 31) /* checking our repair work */
 
 /* Metadata scrubbers */