[PATCH] btrfs-progs: properly format btrfs_header in btrfs_create_root()

* [PATCH] btrfs-progs: properly format btrfs_header in btrfs_create_root()
@ 2021-09-23 15:29 Naohiro Aota
  2021-09-23 19:22 ` David Sterba
  0 siblings, 1 reply; 2+ messages in thread
From: Naohiro Aota @ 2021-09-23 15:29 UTC (permalink / raw)
  To: linux-btrfs; +Cc: David Sterba, Naohiro Aota, Johannes Thumshirn

Enabling quota on zoned btrfs hits the following ASSERT().

    $ mkfs.btrfs -f -d single -m single -R quota /dev/nullb0
    btrfs-progs v5.11
    See http://btrfs.wiki.kernel.org for more information.

    Zoned: /dev/nullb0: host-managed device detected, setting zoned feature
    Resetting device zones /dev/nullb0 (1600 zones) ...
    bad tree block 25395200, bytenr mismatch, want=25395200, have=0
    kernel-shared/disk-io.c:549: write_tree_block: BUG_ON `1` triggered, value 1
    ./mkfs.btrfs(+0x26aaa)[0x564d1a7ccaaa]
    ./mkfs.btrfs(write_tree_block+0xb8)[0x564d1a7cee29]
    ./mkfs.btrfs(__commit_transaction+0x91)[0x564d1a7e3740]
    ./mkfs.btrfs(btrfs_commit_transaction+0x135)[0x564d1a7e39aa]
    ./mkfs.btrfs(main+0x1fe9)[0x564d1a7b442a]
    /lib64/libc.so.6(__libc_start_main+0xcd)[0x7f36377d37fd]
    ./mkfs.btrfs(_start+0x2a)[0x564d1a7b1fda]
    zsh: IOT instruction  sudo ./mkfs.btrfs -f -d single -m single -R quota /dev/nullb0

The issue occur because btrfs_create_root() is not formatting the root node
properly. This is fine on regular btrfs, because it's fortunately reusing
an once freed buffer. As the previous tree node allocation kindly formatted
the header, it will see the proper bytenr and pass the checks.

However, we never reuse an once freed buffer on zoned btrfs. As a result,
we have zero-filled bytenr, FSID, and chunk-tree UUID, hitting the ASSERTs
in check_tree_block().

Reported-by: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
---
 kernel-shared/ctree.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel-shared/ctree.c b/kernel-shared/ctree.c
index 6e9358cbac55..21e5414965e7 100644
--- a/kernel-shared/ctree.c
+++ b/kernel-shared/ctree.c
@@ -237,11 +237,16 @@ int btrfs_create_root(struct btrfs_trans_handle *trans,
 	}
 	new_root->node = node;
 
+	memset_extent_buffer(node, 0, 0, sizeof(struct btrfs_header));
+	btrfs_set_header_bytenr(node, node->start);
 	btrfs_set_header_generation(node, trans->transid);
 	btrfs_set_header_backref_rev(node, BTRFS_MIXED_BACKREF_REV);
-	btrfs_clear_header_flag(node,
-			BTRFS_HEADER_FLAG_RELOC | BTRFS_HEADER_FLAG_WRITTEN);
 	btrfs_set_header_owner(node, objectid);
+	write_extent_buffer(node, fs_info->fs_devices->metadata_uuid,
+			    btrfs_header_fsid(), BTRFS_FSID_SIZE);
+	write_extent_buffer(node, fs_info->chunk_tree_uuid,
+			    btrfs_header_chunk_tree_uuid(node),
+			    BTRFS_UUID_SIZE);
 	btrfs_set_header_nritems(node, 0);
 	btrfs_set_header_level(node, 0);
 	ret = btrfs_inc_ref(trans, new_root, node, 0);
-- 
2.33.0


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