FAILED: patch "[PATCH] btrfs: Use real device structure to verify dev extent" failed to apply to 4.20-stable tree

The patch below does not apply to the 4.20-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1b3922a8bc74231f9a767d1be6d9a061a4d4eeab Mon Sep 17 00:00:00 2001
From: Qu Wenruo <[email protected]>
Date: Tue, 8 Jan 2019 14:08:18 +0800
Subject: [PATCH] btrfs: Use real device structure to verify dev extent

[BUG]
Linux v5.0-rc1 will fail fstests/btrfs/163 with the following kernel message:

BTRFS error (device dm-6): dev extent devid 1 physical offset 13631488 len 8388608 is beyond device boundary 0 BTRFS error (device dm-6): failed to verify dev extents against chunks: -117
BTRFS error (device dm-6): open_ctree failed

[CAUSE]
Commit cf90d884b347 ("btrfs: Introduce mount time chunk <-> dev extent mapping check") introduced strict check on dev extents.

We use btrfs_find_device() with dev uuid and fs uuid set to NULL, and only dependent on @devid to find the real device.

For seed devices, we call clone_fs_devices() in open_seed_devices() to allow us search seed devices directly.

However clone_fs_devices() just populates devices with devid and dev uuid, without populating other essential members, like disk_total_bytes.

This makes any device returned by btrfs_find_device(fs_info, devid, NULL, NULL) is just a dummy, with 0 disk_total_bytes, and any dev extents on the seed device will not pass the device boundary check.

[FIX]
This patch will try to verify the device returned by btrfs_find_device() and if it's a dummy then re-search in seed devices.

index 2576b1a379c9..3e4f8f88353e 100644
@@ -7825,6 +7825,18 @@ static int verify_one_dev_extent(struct btrfs_fs_info *fs_info,
 		ret = -EUCLEAN;
 		goto out;
 	}
+
+	/* It's possible this device is a dummy for seed device */
+	if (dev->disk_total_bytes == 0) {
+		dev = find_device(fs_info->fs_devices->seed, devid, NULL);
+		if (!dev) {
+			btrfs_err(fs_info, "failed to find seed devid %llu",
+				  devid);
+			ret = -EUCLEAN;
+			goto out;
+		}
+	}
+
 	if (physical_offset + physical_len > dev->disk_total_bytes) {
 		btrfs_err(fs_info,
 "dev extent devid %llu physical offset %llu len %llu is beyond device boundary %llu",