[PATCH 2/2] btrfs: Validate btrfs_super_block::log_root_transid

[Qu Wenruo <wqu@suse.com>]

So we can detect log root related problem early and report the error
more meaningfully other than hitting it log root read time.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/disk-io.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5124c15705ce..34c68401c6bc 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2408,6 +2408,7 @@ static int validate_super(struct btrfs_fs_info *fs_info,
 {
 	u64 nodesize = btrfs_super_nodesize(sb);
 	u64 sectorsize = btrfs_super_sectorsize(sb);
+	u64 generation;
 	int ret = 0;
 
 	if (btrfs_super_magic(sb) != BTRFS_MAGIC) {
@@ -2534,21 +2535,36 @@ static int validate_super(struct btrfs_fs_info *fs_info,
 		ret = -EINVAL;
 	}
 
+	generation = btrfs_super_generation(sb);
 	/*
 	 * The generation is a global counter, we'll trust it more than the others
 	 * but it's still possible that it's the one that's wrong.
 	 */
-	if (btrfs_super_generation(sb) < btrfs_super_chunk_root_generation(sb))
+	if (generation < btrfs_super_chunk_root_generation(sb))
 		btrfs_warn(fs_info,
 			"suspicious: generation < chunk_root_generation: %llu < %llu",
-			btrfs_super_generation(sb),
-			btrfs_super_chunk_root_generation(sb));
-	if (btrfs_super_generation(sb) < btrfs_super_cache_generation(sb)
+			generation, btrfs_super_chunk_root_generation(sb));
+	if (generation < btrfs_super_cache_generation(sb)
 	    && btrfs_super_cache_generation(sb) != (u64)-1)
 		btrfs_warn(fs_info,
 			"suspicious: generation < cache_generation: %llu < %llu",
-			btrfs_super_generation(sb),
-			btrfs_super_cache_generation(sb));
+			generation, btrfs_super_cache_generation(sb));
+
+	/*
+	 * Check log root transid against super block generation.
+	 *
+	 * Older kernel doesn't populate log_root_transid, only need to check
+	 * it when it's not zero.
+	 * Since replaying suspicious log tree can cause serious problem, refuse
+	 * to mount if it doesn't match.
+	 */
+	if (btrfs_super_log_root_transid(sb) &&
+	    btrfs_super_log_root_transid(sb) != generation + 1) {
+		btrfs_err(fs_info,
+	"bad log tree, log_root_transid != generation + 1: %llu != %llu + 1",
+			  btrfs_super_log_root_transid(sb), generation);
+		ret = -EINVAL;
+	}
 
 	return ret;
 }
-- 
2.19.0