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    SubjectRe: inode_unused list corruption in 2.4.26 - spin_lock problem?
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    On Wed, 23 Jun 2004, Chris Caputo wrote:
    > On Mon, 21 Jun 2004, Trond Myklebust wrote:
    > > På su , 20/06/2004 klokka 20:45, skreiv Marcelo Tosatti:
    > > > Lets see if I get this right, while we drop the lock in iput to call
    > > > write_inode_now() an iget happens, possibly from write_inode_now itself
    > > > (sync_one->__iget) causing the inode->i_list to be added to to inode_in_use.
    > > > But then the call returns, locks inode_lock, decreases inodes_stat.nr_unused--
    > > > and deletes the inode from the inode_in_use and adds to inode_unused.
    > > >
    > > > AFAICS its an inode with i_count==1 in the unused list, which does not
    > > > mean "list corruption", right? Am I missing something here?
    > >
    > > Yes. Please don't forget that the inode is still hashed and is not yet
    > > marked as FREEING: find_inode() can grab it on behalf of some other
    > > process as soon as we drop that spinlock inside iput(). Then we have the
    > > calls to clear_inode() + destroy_inode() just a few lines further down.
    > > ;-)
    > >
    > > If the above scenario ever does occur, it will cause random Oopses for
    > > third party processes. Since we do not see this too often, my guess is
    > > that the write_inode_now() path must be very rarely (or never?) called.
    > >
    > > > If you are indeed right all 2.4.x versions contain this bug.
    > >
    > > ...and all 2.6.x versions...
    > >
    > > I'm not saying this is the same problem that Chris is seeing, but I am
    > > failing to see how iput() is safe as it stands right now. Please
    > > enlighten me if I'm missing something.
    >
    > I think this is a different (albeit apparently valid) problem. In my case
    > MS_ACTIVE (in iput() below) will be set since I am not unmounting a volume
    > and so I believe iput() will return immediately after adding the inode to
    > the unused list.
    >
    > That said, I have added your patch to my test setup in case it helps.

    I was able to duplicate the problem I am seeing even with Trond's patch
    applied. So the patch potentially solves a different problem but not the
    one I am seeing.

    Chris

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