MFC r316760:

Fix vdev_geom_attach_by_guids for partitioned disks

When opening a vdev whose path is unknown, vdev_geom must find a geom
provider with a label whose guids match the desired vdev. However, due to
partitioning, it is possible that two non-synonomous providers will share
some labels. For example, if the first partition starts at the beginning of
the drive, then ada0 and ada0p1 will share the first label. More troubling,
if the last partition runs to the end of the drive, then ada0p3 and ada0
will share the last label. If vdev_geom opens ada0 when it should've opened
ada0p3, then the pool won't be readable. If it opens ada0 when it should've
opened ada0p1, then it will corrupt some other partition when it writes the
3rd and 4th labels.

The easiest way to reproduce this problem is to install a mirrored root pool
with the default partition layout, then swap the positions of the two boot
drives and reboot.  Whether the bug manifests depends on the order in which
geom lists its providers, which is arbitrary.

Fix this situation by modifying the search algorithm to prefer geom
providers that have all four labels intact. If no such provider exists, then
open whichever provider has the most.

Reviewed by:	mav
Sponsored by:	Spectra Logic Corp
Differential Revision:	https://reviews.freebsd.org/D10365

1 files changed, 44 insertions, 31 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
index 5a78b9e..6fc03f4 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
@@ -402,12 +402,17 @@ vdev_geom_io(struct g_consumer *cp, int *cmds, void **datas, off_t *offsets,
 	kmem_free(bios, bios_size);
 }
 
+/* 
+ * Read the vdev config from a device.  Return the number of valid labels that
+ * were found.  The vdev config will be returned in config if and only if at
+ * least one valid label was found.
+ */
 static int
 vdev_geom_read_config(struct g_consumer *cp, nvlist_t **config)
 {
 	struct g_provider *pp;
 	vdev_phys_t *vdev_lists[VDEV_LABELS];
-	char *p, *buf;
+	char *buf;
 	size_t buflen;
 	uint64_t psize, state, txg;
 	off_t offsets[VDEV_LABELS];
@@ -415,7 +420,7 @@ vdev_geom_read_config(struct g_consumer *cp, nvlist_t **config)
 	off_t sizes[VDEV_LABELS];
 	int cmds[VDEV_LABELS];
 	int errors[VDEV_LABELS];
-	int l, len;
+	int l, nlabels;
 
 	g_topology_assert_not();
 
@@ -446,6 +451,7 @@ vdev_geom_read_config(struct g_consumer *cp, nvlist_t **config)
 	    VDEV_LABELS);
 
 	/* Parse the labels */
+	nlabels = 0;
 	for (l = 0; l < VDEV_LABELS; l++) {
 		if (errors[l] != 0)
 			continue;
@@ -471,14 +477,14 @@ vdev_geom_read_config(struct g_consumer *cp, nvlist_t **config)
 			continue;
 		}
 
-		break;
+		nlabels++;
 	}
 
 	/* Free the label storage */
 	for (l = 0; l < VDEV_LABELS; l++)
 		kmem_free(vdev_lists[l], size);
 
-	return (*config == NULL ? ENOENT : 0);
+	return (nlabels);
 }
 
 static void
@@ -561,7 +567,7 @@ vdev_geom_read_pool_label(const char *name,
 	struct g_consumer *zcp;
 	nvlist_t *vdev_cfg;
 	uint64_t pool_guid;
-	int error;
+	int error, nlabels;
 
 	DROP_GIANT();
 	g_topology_lock();
@@ -582,10 +588,10 @@ vdev_geom_read_pool_label(const char *name,
 				if (zcp == NULL)
 					continue;
 				g_topology_unlock();
-				error = vdev_geom_read_config(zcp, &vdev_cfg);
+				nlabels = vdev_geom_read_config(zcp, &vdev_cfg);
 				g_topology_lock();
 				vdev_geom_detach(zcp, B_TRUE);
-				if (error)
+				if (nlabels == 0)
 					continue;
 				ZFS_LOG(1, "successfully read vdev config");
 
@@ -601,9 +607,13 @@ vdev_geom_read_pool_label(const char *name,
 }
 
 enum match {
-	NO_MATCH,
-	TOP_MATCH,
-	FULL_MATCH
+	NO_MATCH = 0,		/* No matching labels found */
+	TOPGUID_MATCH = 1,	/* Labels match top guid, not vdev guid*/
+	ZERO_MATCH = 1,		/* Should never be returned */
+	ONE_MATCH = 2,		/* 1 label matching the vdev_guid */
+	TWO_MATCH = 3,		/* 2 label matching the vdev_guid */
+	THREE_MATCH = 4,	/* 3 label matching the vdev_guid */
+	FULL_MATCH = 5		/* all labels match the vdev_guid */
 };
 
 static enum match
@@ -612,6 +622,7 @@ vdev_attach_ok(vdev_t *vd, struct g_provider *pp)
 	nvlist_t *config;
 	uint64_t pool_guid, top_guid, vdev_guid;
 	struct g_consumer *cp;
+	int nlabels;
 
 	cp = vdev_geom_attach(pp, NULL);
 	if (cp == NULL) {
@@ -620,7 +631,8 @@ vdev_attach_ok(vdev_t *vd, struct g_provider *pp)
 		return (NO_MATCH);
 	}
 	g_topology_unlock();
-	if (vdev_geom_read_config(cp, &config) != 0) {
+	nlabels = vdev_geom_read_config(cp, &config);
+	if (nlabels == 0) {
 		g_topology_lock();
 		vdev_geom_detach(cp, B_TRUE);
 		ZFS_LOG(1, "Unable to read config from %s.", pp->name);
@@ -655,10 +667,10 @@ vdev_attach_ok(vdev_t *vd, struct g_provider *pp)
 	 */
 	if (vdev_guid == vd->vdev_guid) {
 		ZFS_LOG(1, "guids match for provider %s.", pp->name);
-		return (FULL_MATCH);
+		return (ZERO_MATCH + nlabels);
 	} else if (top_guid == vd->vdev_guid && vd == vd->vdev_top) {
 		ZFS_LOG(1, "top vdev guid match for provider %s.", pp->name);
-		return (TOP_MATCH);
+		return (TOPGUID_MATCH);
 	}
 	ZFS_LOG(1, "vdev guid mismatch for provider %s: %ju != %ju.",
 	    pp->name, (uintmax_t)vd->vdev_guid, (uintmax_t)vdev_guid);
@@ -670,13 +682,15 @@ vdev_geom_attach_by_guids(vdev_t *vd)
 {
 	struct g_class *mp;
 	struct g_geom *gp;
-	struct g_provider *pp;
+	struct g_provider *pp, *best_pp;
 	struct g_consumer *cp;
-	enum match m;
+	enum match match, best_match;
 
 	g_topology_assert();
 
 	cp = NULL;
+	best_pp = NULL;
+	best_match = NO_MATCH;
 	LIST_FOREACH(mp, &g_classes, class) {
 		if (mp == &zfs_vdev_class)
 			continue;
@@ -684,26 +698,25 @@ vdev_geom_attach_by_guids(vdev_t *vd)
 			if (gp->flags & G_GEOM_WITHER)
 				continue;
 			LIST_FOREACH(pp, &gp->provider, provider) {
-				m = vdev_attach_ok(vd, pp);
-				if (m == NO_MATCH)
-					continue;
-				if (cp != NULL) {
-					if (m == FULL_MATCH)
-						vdev_geom_detach(cp, B_TRUE);
-					else
-						continue;
+				match = vdev_attach_ok(vd, pp);
+				if (match > best_match) {
+					best_match = match;
+					best_pp = pp;
 				}
-				cp = vdev_geom_attach(pp, vd);
-				if (cp == NULL) {
-					printf("ZFS WARNING: Unable to "
-					    "attach to %s.\n", pp->name);
-					continue;
-				}
-				if (m == FULL_MATCH)
-					return (cp);
+				if (match == FULL_MATCH)
+					goto out;
 			}
 		}
 	}
+
+out:
+	if (best_pp) {
+		cp = vdev_geom_attach(best_pp, vd);
+		if (cp == NULL) {
+			printf("ZFS WARNING: Unable to attach to %s.\n",
+			    best_pp->name);
+		}
+	}
 	return (cp);
 }