Remove races from scrub / resilver tests

Currently, several tests in the ZFS Test Suite that attempt to
test scrub and resilver behavior occasionally fail. A big reason
for this is that these tests use a combination of zinject and
zfs_scan_vdev_limit to attempt to slow these operations enough
to verify their test commands. This method works most of the time,
but provides no guarantees and leads to flaky behavior. This patch
adds a new tunable, zfs_scan_suspend_progress, that ensures that
scans make no progress, guaranteeing that tests can be run without
racing.

This patch also changes zfs_remove_max_bytes_pause to match this
new tunable. This provides some consistency between these two
similar tunables and ensures that the tunable will not misbehave
on 32-bit systems.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Giuseppe Di Natale <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>
Signed-off-by: Tom Caputi <[email protected]>
Closes #8111

1 files changed, 26 insertions, 0 deletions

diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c
index 61d42deca..d9d9900a2 100644
--- a/module/zfs/dsl_scan.c
+++ b/module/zfs/dsl_scan.c
@@ -169,6 +169,7 @@ int zfs_obsolete_min_time_ms = 500; /* min millisecs to obsolete per txg */
 int zfs_free_min_time_ms = 1000; /* min millisecs to free per txg */
 int zfs_resilver_min_time_ms = 3000; /* min millisecs to resilver per txg */
 int zfs_scan_checkpoint_intval = 7200; /* in seconds */
+int zfs_scan_suspend_progress = 0; /* set to prevent scans from progressing */
 int zfs_no_scrub_io = B_FALSE; /* set to disable scrub i/o */
 int zfs_no_scrub_prefetch = B_FALSE; /* set to disable scrub prefetch */
 enum ddt_class zfs_scrub_ddt_class_max = DDT_CLASS_DUPLICATE;
@@ -3357,6 +3358,27 @@ dsl_scan_sync(dsl_pool_t *dp, dmu_tx_t *tx)
 		return;
 
 	/*
+	 * zfs_scan_suspend_progress can be set to disable scan progress.
+	 * We don't want to spin the txg_sync thread, so we add a delay
+	 * here to simulate the time spent doing a scan. This is mostly
+	 * useful for testing and debugging.
+	 */
+	if (zfs_scan_suspend_progress) {
+		uint64_t scan_time_ns = gethrtime() - scn->scn_sync_start_time;
+		int mintime = (scn->scn_phys.scn_func == POOL_SCAN_RESILVER) ?
+		    zfs_resilver_min_time_ms : zfs_scrub_min_time_ms;
+
+		while (zfs_scan_suspend_progress &&
+		    !txg_sync_waiting(scn->scn_dp) &&
+		    !spa_shutting_down(scn->scn_dp->dp_spa) &&
+		    NSEC2MSEC(scan_time_ns) < mintime) {
+			delay(hz);
+			scan_time_ns = gethrtime() - scn->scn_sync_start_time;
+		}
+		return;
+	}
+
+	/*
 	 * It is possible to switch from unsorted to sorted at any time,
 	 * but afterwards the scan will remain sorted unless reloaded from
 	 * a checkpoint after a reboot.
@@ -4070,6 +4092,10 @@ MODULE_PARM_DESC(zfs_free_min_time_ms, "Min millisecs to free per txg");
 module_param(zfs_resilver_min_time_ms, int, 0644);
 MODULE_PARM_DESC(zfs_resilver_min_time_ms, "Min millisecs to resilver per txg");
 
+module_param(zfs_scan_suspend_progress, int, 0644);
+MODULE_PARM_DESC(zfs_scan_suspend_progress,
+	"Set to prevent scans from progressing");
+
 module_param(zfs_no_scrub_io, int, 0644);
 MODULE_PARM_DESC(zfs_no_scrub_io, "Set to disable scrub I/O");