btrfs: zoned: do not enable async discard

The zoned mode need to reset a zone before using it. We rely on btrfs's
original discard functionality (discarding unused block group range) to do
the resetting.

While the commit 63a7cb1307 ("btrfs: auto enable discard=async when
possible") made the discard done in an async manner, a zoned reset do not
need to be async, as it is fast enough.

Even worth, delaying zone rests prevents using those zones again. So, let's
disable async discard on the zoned mode.

Fixes: 63a7cb1307 ("btrfs: auto enable discard=async when possible")
CC: stable@vger.kernel.org # 6.3+
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update message text ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -3438,11 +3438,16 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	 * For devices supporting discard turn on discard=async automatically,
 	 * unless it's already set or disabled. This could be turned off by
 	 * nodiscard for the same mount.
+	 *
+	 * The zoned mode piggy backs on the discard functionality for
+	 * resetting a zone. There is no reason to delay the zone reset as it is
+	 * fast enough. So, do not enable async discard for zoned mode.
 	 */
 	if (!(btrfs_test_opt(fs_info, DISCARD_SYNC) ||
 	      btrfs_test_opt(fs_info, DISCARD_ASYNC) ||
 	      btrfs_test_opt(fs_info, NODISCARD)) &&
-	    fs_info->fs_devices->discardable) {
+	    fs_info->fs_devices->discardable &&
+	    !btrfs_is_zoned(fs_info)) {
 		btrfs_set_and_info(fs_info, DISCARD_ASYNC,
 				   "auto enabling async discard");
 	}

fs/btrfs/zoned.c

@@ -805,6 +805,9 @@ int btrfs_check_mountopts_zoned(struct btrfs_fs_info *info)
 		return -EINVAL;
 	}
 
+	btrfs_clear_and_info(info, DISCARD_ASYNC,
+			"zoned: async discard ignored and disabled for zoned mode");
+
 	return 0;
 }