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    SubjectRe: [PATCH 3/5] ext4: ext4_mark_recovery_complete() doesn't need to use lock_super
    On Sun, Apr 26, 2009 at 03:07:14AM -0400, Christoph Hellwig wrote:
    > On Sat, Apr 25, 2009 at 11:49:23PM -0400, Theodore Ts'o wrote:
    > > The function ext4_mark_recovery_complete() is called from two call
    > > paths: either (a) while mounting the filesystem, in which case there's
    > > no danger of any other CPU calling write_super() until the mount is
    > > completed, and (b) while remounting the filesystem read-write, in
    > > which case the fs core has already locked the superblock, and in any
    > > case write_super() wouldn't be called until the filesystem is
    > > successfully changed from being mounted read-only to read-write.
    >
    > Currently ext4_remount releases/reqacquires lock_super around
    > ext4_mark_recovery_complete, and unfortunately currently ->write_super
    > can be called on a r/o filesystem (that's why we have the MS_RDONLY
    > checks in all instance, I plan to clean that mess up).

    That's true, but the patch also takes out the release/reacquire in in
    ext4_remount (which was particularly ugly, belch). So even if
    write_super gets called on an r/o filesystem (why?!?), we should be
    safe because remount will hold lock_super() throughout the entire
    remount operation.

    We could delay this cleanup until you clean the mess with write_super,
    but I don't think it would be harmful in removing the
    lock_super()/unlock_super() pair in ext4_mark_recovery_complete(), and
    the unlock_super()/lock_super() pair in ext4_remount before then. Am
    I missing something?

    - Ted


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