MFV r251626:

ZFS event processing should work on R/O root filesystems

Illumos ZFS issues:
  3749 zfs event processing should work on R/O root filesystems

MFC after:      2 weeks

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa.c

@@ -88,6 +88,12 @@ TUNABLE_INT("vfs.zfs.check_hostid", &check_hostid);
 SYSCTL_INT(_vfs_zfs, OID_AUTO, check_hostid, CTLFLAG_RW, &check_hostid, 0,
     "Check hostid on import?");
 
+/*
+ * The interval, in seconds, at which failed configuration cache file writes
+ * should be retried.
+ */
+static int zfs_ccw_retry_interval = 300;
+
 typedef enum zti_modes {
 	zti_mode_fixed,			/* value is # of threads (min 1) */
 	zti_mode_online_percent,	/* value is % of online CPUs */
@@ -5852,13 +5858,34 @@ spa_async_resume(spa_t *spa)
 	mutex_exit(&spa->spa_async_lock);
 }
 
+static boolean_t
+spa_async_tasks_pending(spa_t *spa)
+{
+	uint_t non_config_tasks;
+	uint_t config_task;
+	boolean_t config_task_suspended;
+
+	non_config_tasks = spa->spa_async_tasks & ~SPA_ASYNC_CONFIG_UPDATE;
+	config_task = spa->spa_async_tasks & SPA_ASYNC_CONFIG_UPDATE;
+	if (spa->spa_ccw_fail_time == 0) {
+		config_task_suspended = B_FALSE;
+	} else {
+		config_task_suspended =
+		    (gethrtime() - spa->spa_ccw_fail_time) <
+		    (zfs_ccw_retry_interval * NANOSEC);
+	}
+
+	return (non_config_tasks || (config_task && !config_task_suspended));
+}
+
 static void
 spa_async_dispatch(spa_t *spa)
 {
 	mutex_enter(&spa->spa_async_lock);
-	if (spa->spa_async_tasks && !spa->spa_async_suspended &&
+	if (spa_async_tasks_pending(spa) &&
+	    !spa->spa_async_suspended &&
 	    spa->spa_async_thread == NULL &&
-	    rootdir != NULL && !vn_is_readonly(rootdir))
+	    rootdir != NULL)
 		spa->spa_async_thread = thread_create(NULL, 0,
 		    spa_async_thread, spa, 0, &p0, TS_RUN, maxclsyspri);
 	mutex_exit(&spa->spa_async_lock);

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_config.c

@@ -27,6 +27,7 @@
 
 #include <sys/zfs_context.h>
 #include <sys/spa.h>
+#include <sys/fm/fs/zfs.h>
 #include <sys/spa_impl.h>
 #include <sys/nvpair.h>
 #include <sys/uio.h>
@@ -139,7 +140,7 @@ spa_config_load(void)
 	kobj_close_file(file);
 }
 
-static void
+static int
 spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 {
 	size_t buflen;
@@ -147,13 +148,14 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 	vnode_t *vp;
 	int oflags = FWRITE | FTRUNC | FCREAT | FOFFMAX;
 	char *temp;
+	int err;
 
 	/*
 	 * If the nvlist is empty (NULL), then remove the old cachefile.
 	 */
 	if (nvl == NULL) {
-		(void) vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
-		return;
+		err = vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
+		return (err);
 	}
 
 	/*
@@ -174,12 +176,14 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 	 */
 	(void) snprintf(temp, MAXPATHLEN, "%s.tmp", dp->scd_path);
 
-	if (vn_open(temp, UIO_SYSSPACE, oflags, 0644, &vp, CRCREAT, 0) == 0) {
-		if (vn_rdwr(UIO_WRITE, vp, buf, buflen, 0, UIO_SYSSPACE,
-		    0, RLIM64_INFINITY, kcred, NULL) == 0 &&
-		    VOP_FSYNC(vp, FSYNC, kcred, NULL) == 0) {
-			(void) vn_rename(temp, dp->scd_path, UIO_SYSSPACE);
-		}
+	err = vn_open(temp, UIO_SYSSPACE, oflags, 0644, &vp, CRCREAT, 0);
+	if (err == 0) {
+		err = vn_rdwr(UIO_WRITE, vp, buf, buflen, 0, UIO_SYSSPACE,
+		    0, RLIM64_INFINITY, kcred, NULL);
+		if (err == 0)
+			err = VOP_FSYNC(vp, FSYNC, kcred, NULL);
+		if (err == 0)
+			err = vn_rename(temp, dp->scd_path, UIO_SYSSPACE);
 		(void) VOP_CLOSE(vp, oflags, 1, 0, kcred, NULL);
 	}
 
@@ -187,6 +191,7 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 
 	kmem_free(buf, buflen);
 	kmem_free(temp, MAXPATHLEN);
+	return (err);
 }
 
 /*
@@ -198,6 +203,8 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 {
 	spa_config_dirent_t *dp, *tdp;
 	nvlist_t *nvl;
+	boolean_t ccw_failure;
+	int error;
 
 	ASSERT(MUTEX_HELD(&spa_namespace_lock));
 
@@ -209,6 +216,7 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 	 * cachefile is changed, the new one is pushed onto this list, allowing
 	 * us to update previous cachefiles that no longer contain this pool.
 	 */
+	ccw_failure = B_FALSE;
 	for (dp = list_head(&target->spa_config_list); dp != NULL;
 	    dp = list_next(&target->spa_config_list, dp)) {
 		spa_t *spa = NULL;
@@ -249,10 +257,32 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 			mutex_exit(&spa->spa_props_lock);
 		}
 
-		spa_config_write(dp, nvl);
+		error = spa_config_write(dp, nvl);
+		if (error != 0)
+			ccw_failure = B_TRUE;
 		nvlist_free(nvl);
 	}
 
+	if (ccw_failure) {
+		/*
+		 * Keep trying so that configuration data is
+		 * written if/when any temporary filesystem
+		 * resource issues are resolved.
+		 */
+		if (target->spa_ccw_fail_time == 0) {
+			zfs_ereport_post(FM_EREPORT_ZFS_CONFIG_CACHE_WRITE,
+			    target, NULL, NULL, 0, 0);
+		}
+		target->spa_ccw_fail_time = gethrtime();
+		spa_async_request(target, SPA_ASYNC_CONFIG_UPDATE);
+	} else {
+		/*
+		 * Do not rate limit future attempts to update
+		 * the config cache.
+		 */
+		target->spa_ccw_fail_time = 0;
+	}
+
 	/*
 	 * Remove any config entries older than the current one.
 	 */

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa_impl.h

@@ -241,6 +241,7 @@ struct spa {
 	uint64_t	spa_deadman_calls;	/* number of deadman calls */
 	uint64_t	spa_sync_starttime;	/* starting time fo spa_sync */
 	uint64_t	spa_deadman_synctime;	/* deadman expiration timer */
+	hrtime_t	spa_ccw_fail_time;	/* Conf cache write fail time */
 	/*
 	 * spa_refcount & spa_config_lock must be the last elements
 	 * because refcount_t changes size based on compilation options.

sys/cddl/contrib/opensolaris/uts/common/sys/fm/fs/zfs.h

@@ -46,6 +46,7 @@ extern "C" {
 #define	FM_EREPORT_ZFS_IO_FAILURE		"io_failure"
 #define	FM_EREPORT_ZFS_PROBE_FAILURE		"probe_failure"
 #define	FM_EREPORT_ZFS_LOG_REPLAY		"log_replay"
+#define	FM_EREPORT_ZFS_CONFIG_CACHE_WRITE	"config_cache_write"
 
 #define	FM_EREPORT_PAYLOAD_ZFS_POOL		"pool"
 #define	FM_EREPORT_PAYLOAD_ZFS_POOL_FAILMODE	"pool_failmode"