Revert "Illumos 3749 - zfs event processing should work on R/O root filesystems"

This reverts commit b47637ecdc7b647ec5bd9dfca888179eecfaa72d which
introduced a regression in ztest.

$ ./cmd/ztest/ztest -V
5 vdevs, 7 datasets, 23 threads, 300 seconds...
*** Error in `/rpool/home/behlendo/src/git/zfs/cmd/ztest/.libs/lt-ztest':
double free or corruption (fasttop): 0x0000000000d339f0 ***

2 files changed, 20 insertions, 76 deletions

diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index ffefbd345..d7b800adf 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -82,12 +82,6 @@
 #include "zfs_prop.h"
 #include "zfs_comutil.h"
 
-/*
- * 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_BATCH,			/* cpu-intensive; value is ignored */
@@ -5918,34 +5912,13 @@ 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_async_tasks_pending(spa) &&
-	    !spa->spa_async_suspended &&
+	if (spa->spa_async_tasks && !spa->spa_async_suspended &&
 	    spa->spa_async_thread == NULL &&
-	    rootdir != NULL)
+	    rootdir != NULL && !vn_is_readonly(rootdir))
 		spa->spa_async_thread = thread_create(NULL, 0,
 		    spa_async_thread, spa, 0, &p0, TS_RUN, maxclsyspri);
 	mutex_exit(&spa->spa_async_lock);
diff --git a/module/zfs/spa_config.c b/module/zfs/spa_config.c
index 831eca7f5..19432e0a0 100644
--- a/module/zfs/spa_config.c
+++ b/module/zfs/spa_config.c
@@ -26,7 +26,6 @@
  */
 
 #include <sys/spa.h>
-#include <sys/fm/fs/zfs.h>
 #include <sys/spa_impl.h>
 #include <sys/nvpair.h>
 #include <sys/uio.h>
@@ -146,22 +145,22 @@ out:
 	kobj_close_file(file);
 }
 
-static int
+static void
 spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 {
 	size_t buflen;
 	char *buf;
 	vnode_t *vp;
 	int oflags = FWRITE | FTRUNC | FCREAT | FOFFMAX;
+	int error;
 	char *temp;
-	int err;
 
 	/*
 	 * If the nvlist is empty (NULL), then remove the old cachefile.
 	 */
 	if (nvl == NULL) {
-		err = vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
-		return (err);
+		(void) vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
+		return;
 	}
 
 	/*
@@ -182,16 +181,16 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 	 * and overwritten in place.  In the event of an error the file is
 	 * unlinked to make sure we always have a consistent view of the data.
 	 */
-	err = vn_open(dp->scd_path, UIO_SYSSPACE, oflags, 0644, &vp, 0, 0);
-	if (err == 0) {
-		err = vn_rdwr(UIO_WRITE, vp, buf, buflen, 0,
+	error = vn_open(dp->scd_path, UIO_SYSSPACE, oflags, 0644, &vp, 0, 0);
+	if (error == 0) {
+		error = 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 (error == 0)
+			error = VOP_FSYNC(vp, FSYNC, kcred, NULL);
 
 		(void) VOP_CLOSE(vp, oflags, 1, 0, kcred, NULL);
 
-		if (err)
+		if (error)
 			(void) vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
 	}
 #else
@@ -202,16 +201,14 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 	 */
 	(void) snprintf(temp, MAXPATHLEN, "%s.tmp", dp->scd_path);
 
-	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);
+	error = vn_open(temp, UIO_SYSSPACE, oflags, 0644, &vp, CRCREAT, 0);
+	if (error == 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);
+		}
 		(void) VOP_CLOSE(vp, oflags, 1, 0, kcred, NULL);
-		VN_RELE(vp);
 	}
 
 	(void) vn_remove(temp, UIO_SYSSPACE, RMFILE);
@@ -219,7 +216,6 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 
 	vmem_free(buf, buflen);
 	kmem_free(temp, MAXPATHLEN);
-	return (err);
 }
 
 /*
@@ -237,8 +233,6 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 	spa_config_dirent_t *dp, *tdp;
 	nvlist_t *nvl;
 	char *pool_name;
-	boolean_t ccw_failure;
-	int error = 0;
 
 	ASSERT(MUTEX_HELD(&spa_namespace_lock));
 
@@ -250,7 +244,6 @@ 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;
@@ -297,32 +290,10 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 			mutex_exit(&spa->spa_props_lock);
 		}
 
-		error = spa_config_write(dp, nvl);
-		if (error != 0)
-			ccw_failure = B_TRUE;
+		spa_config_write(dp, nvl);
 		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.
 	 */