[Bug 48431] New: ext4_fill_super() reports success even if ext4_mb_init() fails

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https://bugzilla.kernel.org/show_bug.cgi?id=48431

           Summary: ext4_fill_super() reports success even if
                    ext4_mb_init() fails
           Product: File System
           Version: 2.5
    Kernel Version: 3.6
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ext4
        AssignedTo: fs_ext4@kernel-bugs.osdl.org
        ReportedBy: eugene.shatokhin@rosalab.ru
        Regression: No


Created an attachment (id=82361)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=82361)
The patch to fix the problem

If ext4_mb_init() called from ext4_fill_super() (fs/ext4/super.c:3980 in the
current ext4 git tree) fails and returns error code, ext4_fill_super() still
returns 0. 

This happens because the return value of ext4_mb_init() is not assigned to
'ret' in the error path. So the previous value of 'ret' (0) is returned from
ext4_fill_super().

This problem leads to a kernel oops in mount_fs() when the latter tries to
access the struct dentry that the mount() callback returns ("sb = root->d_sb;"
in fs/super.c:1180).

The problem has been revealed with the help of the fault simulation facilities
provided by KEDR Framework.

Attached is a trivial patch that fixes the problem.

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