OpenZFS 8473 - scrub does not detect errors on active spares

Scrubbing is supposed to detect and repair all errors in the pool.
However, it wrongly ignores active spare devices. The problem can
easily be reproduced in OpenZFS at git rev 0ef125d with these
commands:

    truncate -s 64m /tmp/a /tmp/b /tmp/c
    sudo zpool create testpool mirror /tmp/a /tmp/b spare /tmp/c
    sudo zpool replace testpool /tmp/a /tmp/c
    /bin/dd if=/dev/zero bs=1024k count=63 oseek=1 conv=notrunc of=/tmp/c
    sync
    sudo zpool scrub testpool
    zpool status testpool # Will show 0 errors, which is wrong
    sudo zpool offline testpool /tmp/a
    sudo zpool scrub testpool
    zpool status testpool # Will show errors on /tmp/c,
                          # which should've already been fixed

FreeBSD head is partially affected: the first scrub will detect
some errors, but the second scrub will detect more.  This same
test was run on Linux before applying the fix and the FreeBSD
head behavior was observed.

Authored by: asomers <[email protected]>
Reviewed by: Andy Stormont <[email protected]>
Reviewed by: Matt Ahrens <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Approved by: Richard Lowe <[email protected]>
Ported-by: Brian Behlendorf <[email protected]>
Sponsored by: Spectra Logic Corp

OpenZFS-issue: https://www.illumos.org/issues/8473
FreeBSD-commit: https://github.com/freebsd/freebsd/commit/e20ec8879
OpenZFS-commit: https://github.com/illumos/illumos-gate/commit/554675ee
Closes #8251

1 files changed, 41 insertions, 8 deletions

diff --git a/module/zfs/vdev_mirror.c b/module/zfs/vdev_mirror.c
index b45c05db2..a92d956cd 100644
--- a/module/zfs/vdev_mirror.c
+++ b/module/zfs/vdev_mirror.c
@@ -29,6 +29,9 @@
 
 #include <sys/zfs_context.h>
 #include <sys/spa.h>
+#include <sys/spa_impl.h>
+#include <sys/dsl_pool.h>
+#include <sys/dsl_scan.h>
 #include <sys/vdev_impl.h>
 #include <sys/zio.h>
 #include <sys/abd.h>
@@ -111,7 +114,7 @@ typedef struct mirror_map {
 	int		*mm_preferred;
 	int		mm_preferred_cnt;
 	int		mm_children;
-	boolean_t	mm_replacing;
+	boolean_t	mm_resilvering;
 	boolean_t	mm_root;
 	mirror_child_t	mm_child[];
 } mirror_map_t;
@@ -145,13 +148,13 @@ vdev_mirror_map_size(int children)
 }
 
 static inline mirror_map_t *
-vdev_mirror_map_alloc(int children, boolean_t replacing, boolean_t root)
+vdev_mirror_map_alloc(int children, boolean_t resilvering, boolean_t root)
 {
 	mirror_map_t *mm;
 
 	mm = kmem_zalloc(vdev_mirror_map_size(children), KM_SLEEP);
 	mm->mm_children = children;
-	mm->mm_replacing = replacing;
+	mm->mm_resilvering = resilvering;
 	mm->mm_root = root;
 	mm->mm_preferred = (int *)((uintptr_t)mm +
 	    offsetof(mirror_map_t, mm_child[children]));
@@ -285,9 +288,39 @@ vdev_mirror_map_init(zio_t *zio)
 			mc->mc_offset = DVA_GET_OFFSET(&dva[c]);
 		}
 	} else {
-		mm = vdev_mirror_map_alloc(vd->vdev_children,
-		    (vd->vdev_ops == &vdev_replacing_ops ||
-		    vd->vdev_ops == &vdev_spare_ops), B_FALSE);
+		/*
+		 * If we are resilvering, then we should handle scrub reads
+		 * differently; we shouldn't issue them to the resilvering
+		 * device because it might not have those blocks.
+		 *
+		 * We are resilvering iff:
+		 * 1) We are a replacing vdev (ie our name is "replacing-1" or
+		 *    "spare-1" or something like that), and
+		 * 2) The pool is currently being resilvered.
+		 *
+		 * We cannot simply check vd->vdev_resilver_txg, because it's
+		 * not set in this path.
+		 *
+		 * Nor can we just check our vdev_ops; there are cases (such as
+		 * when a user types "zpool replace pool odev spare_dev" and
+		 * spare_dev is in the spare list, or when a spare device is
+		 * automatically used to replace a DEGRADED device) when
+		 * resilvering is complete but both the original vdev and the
+		 * spare vdev remain in the pool.  That behavior is intentional.
+		 * It helps implement the policy that a spare should be
+		 * automatically removed from the pool after the user replaces
+		 * the device that originally failed.
+		 *
+		 * If a spa load is in progress, then spa_dsl_pool may be
+		 * uninitialized.  But we shouldn't be resilvering during a spa
+		 * load anyway.
+		 */
+		boolean_t replacing = (vd->vdev_ops == &vdev_replacing_ops ||
+		    vd->vdev_ops == &vdev_spare_ops) &&
+		    spa_load_state(vd->vdev_spa) == SPA_LOAD_NONE &&
+		    dsl_scan_resilvering(vd->vdev_spa->spa_dsl_pool);
+		mm = vdev_mirror_map_alloc(vd->vdev_children, replacing,
+		    B_FALSE);
 		for (c = 0; c < mm->mm_children; c++) {
 			mc = &mm->mm_child[c];
 			mc->mc_vd = vd->vdev_child[c];
@@ -521,7 +554,7 @@ vdev_mirror_io_start(zio_t *zio)
 
 	if (zio->io_type == ZIO_TYPE_READ) {
 		if (zio->io_bp != NULL &&
-		    (zio->io_flags & ZIO_FLAG_SCRUB) && !mm->mm_replacing) {
+		    (zio->io_flags & ZIO_FLAG_SCRUB) && !mm->mm_resilvering) {
 			/*
 			 * For scrubbing reads (if we can verify the
 			 * checksum here, as indicated by io_bp being
@@ -663,7 +696,7 @@ vdev_mirror_io_done(zio_t *zio)
 	if (good_copies && spa_writeable(zio->io_spa) &&
 	    (unexpected_errors ||
 	    (zio->io_flags & ZIO_FLAG_RESILVER) ||
-	    ((zio->io_flags & ZIO_FLAG_SCRUB) && mm->mm_replacing))) {
+	    ((zio->io_flags & ZIO_FLAG_SCRUB) && mm->mm_resilvering))) {
 		/*
 		 * Use the good data we have in hand to repair damaged children.
 		 */