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 <w...@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

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