zfs_sync: remove support for impossible scenarios

The superblock pointer will always be set, as will z_log, so remove code
supporting cases that can't occur (on Linux at least).

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Paul Dagnelie <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Closes #17420

Author: robn

module/os/linux/zfs/zfs_vfsops.c

@@ -265,6 +265,7 @@ zfs_sync(struct super_block *sb, int wait, cred_t *cr)
 {
 	(void) cr;
 	zfsvfs_t *zfsvfs = sb->s_fs_info;
+	ASSERT3P(zfsvfs, !=, NULL);
 
 	/*
 	 * Semantically, the only requirement is that the sync be initiated.
@@ -273,39 +274,22 @@ zfs_sync(struct super_block *sb, int wait, cred_t *cr)
 	if (!wait)
 		return (0);
 
-	if (zfsvfs != NULL) {
-		/*
-		 * Sync a specific filesystem.
-		 */
-		dsl_pool_t *dp;
-		int error;
-
-		if ((error = zfs_enter(zfsvfs, FTAG)) != 0)
-			return (error);
-		dp = dmu_objset_pool(zfsvfs->z_os);
-
-		/*
-		 * If the system is shutting down, then skip any
-		 * filesystems which may exist on a suspended pool.
-		 */
-		if (spa_suspended(dp->dp_spa)) {
-			zfs_exit(zfsvfs, FTAG);
-			return (0);
-		}
-
-		if (zfsvfs->z_log != NULL)
-			zil_commit(zfsvfs->z_log, 0);
+	int err = zfs_enter(zfsvfs, FTAG);
+	if (err != 0)
+		return (err);
 
+	/*
+	 * If the system is shutting down, then skip any
+	 * filesystems which may exist on a suspended pool.
+	 */
+	if (spa_suspended(zfsvfs->z_os->os_spa)) {
 		zfs_exit(zfsvfs, FTAG);
-	} else {
-		/*
-		 * Sync all ZFS filesystems.  This is what happens when you
-		 * run sync(1).  Unlike other filesystems, ZFS honors the
-		 * request by waiting for all pools to commit all dirty data.
-		 */
-		spa_sync_allpools();
+		return (0);
 	}
 
+	zil_commit(zfsvfs->z_log, 0);
+	zfs_exit(zfsvfs, FTAG);
+
 	return (0);
 }