Re: inode_unused list corruption in 2.4.26 - spin_lock problem?

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Date:	Fri, 25 Jun 2004 00:47:39 -0700 (PDT)
To: Trond Myklebust <trond.myklebust@fys.uio.no>

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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