[PATCH 3.16 046/366] ext4: do not update s_last_mounted of a frozen fs

[Ben Hutchings]

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Amir Goldstein <amir7...@gmail.com>

commit db6516a5e7ddb6dc72d167b920f2f272596ea22d upstream.

If fs is frozen after mount and before the first file open, the
update of s_last_mounted bypasses freeze protection and prints out
a WARNING splat:

$ mount /vdf
$ fsfreeze -f /vdf
$ cat /vdf/foo

[   31.578555] WARNING: CPU: 1 PID: 1415 at
fs/ext4/ext4_jbd2.c:53 ext4_journal_check_start+0x48/0x82

[   31.614016] Call Trace:
[   31.614997]  __ext4_journal_start_sb+0xe4/0x1a4
[   31.616771]  ? ext4_file_open+0xb6/0x189
[   31.618094]  ext4_file_open+0xb6/0x189

If fs is frozen, skip s_last_mounted update.

[backport hint: to apply to stable tree, need to apply also patches
 vfs: add the sb_start_intwrite_trylock() helper
 ext4: factor out helper ext4_sample_last_mounted()]

Fixes: bc0b0d6d69ee ("ext4: update the s_last_mounted field in the superblock")
Signed-off-by: Amir Goldstein <amir7...@gmail.com>
Signed-off-by: Theodore Ts'o <ty...@mit.edu>
Reviewed-by: Jan Kara <j...@suse.cz>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 fs/ext4/file.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -220,7 +220,7 @@ static int ext4_sample_last_mounted(stru
        if (likely(sbi->s_mount_flags & EXT4_MF_MNTDIR_SAMPLED))
                return 0;
 
-       if (sb->s_flags & MS_RDONLY)
+       if (sb->s_flags & MS_RDONLY || !sb_start_intwrite_trylock(sb))
                return 0;
 
        sbi->s_mount_flags |= EXT4_MF_MNTDIR_SAMPLED;
@@ -234,21 +234,25 @@ static int ext4_sample_last_mounted(stru
        path.mnt = mnt;
        path.dentry = mnt->mnt_root;
        cp = d_path(&path, buf, sizeof(buf));
+       err = 0;
        if (IS_ERR(cp))
-               return 0;
+               goto out;
 
        handle = ext4_journal_start_sb(sb, EXT4_HT_MISC, 1);
+       err = PTR_ERR(handle);
        if (IS_ERR(handle))
-               return PTR_ERR(handle);
+               goto out;
        BUFFER_TRACE(sbi->s_sbh, "get_write_access");
        err = ext4_journal_get_write_access(handle, sbi->s_sbh);
        if (err)
-               goto out;
+               goto out_journal;
        strlcpy(sbi->s_es->s_last_mounted, cp,
                sizeof(sbi->s_es->s_last_mounted));
        ext4_handle_dirty_super(handle, sb);
-out:
+out_journal:
        ext4_journal_stop(handle);
+out:
+       sb_end_intwrite(sb);
        return err;
 }