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From: Amir Goldstein <amir73il@gmail.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Phasip <phasip@gmail.com>, overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: Kernel warnings in fs/inode.c:302 drop_nlink+0x28/0x40
Date: Mon, 23 Mar 2020 19:27:41 +0200
Message-ID: <CAOQ4uxha8XSB62cq=+X-tCdMUnOTrYpJT1YbjxuLhmrFsRM-Pw@mail.gmail.com> (raw)
In-Reply-To: <CAJfpeguKujUqW-z75F+6mCh0uwHF6rz2cK4OWUCFe83QNmaSrQ@mail.gmail.com>

On Mon, Mar 23, 2020 at 4:53 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Mon, Mar 23, 2020 at 3:21 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Mon, Mar 23, 2020 at 2:24 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> > > IDGI. coming from vfs_unlink() and vfs_rename() it doesn't look like
> > > it is possible for victim inode not to have a hashed alias, so the
> > > alias test seems futile.
> >
> > Yeah, needs a comment: both ovl_remove_upper() and
> > ovl_remove_and_whiteout() unhash the dentry before returning, so
> > d_find_alias() will find another hashed dentry or none.
>
> Except that doesn't seem to be true for the overwriting rename case...
>
> Attached patch should work for both.
>

It still looks quite hacky.
Why do we not look at upper->i_nlink in order to fix the situation?

For index=on, there is already code to handle lower hardlink skew case,
including pr_warn and several xfstests (overlay/034 for example).
The check is buried in ovl_nlink_end() => ovl_cleanup_index().
It's keeping overlay i_nlink above upper i_nlink.

In fact, if you change one line in overlay/034 it triggers the reported
bug, so we can just fork this test.

-lowerdir=$OVL_BASE_SCRATCH_MNT/$OVL_LOWER
+lowerdir=$OVL_BASE_SCRATCH_MNT/$OVL_UPPER
 workdir=$OVL_BASE_SCRATCH_MNT/$OVL_WORK

How about adding a check in ovl_nlink_start() to fix overlay i_nlink
below upper i_link?
It would be a valid check for both index=off and on.
I will try to write it up later.

Thanks,
Amir.

  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAFkON1U3cXdXFQYdkoQ3OQU+14GX7C88U6qre58vyfhrrFgKXw@mail.gmail.com>
2020-03-23 12:52 ` Miklos Szeredi
2020-03-23 13:23   ` Amir Goldstein
2020-03-23 14:21     ` Miklos Szeredi
2020-03-23 14:53       ` Miklos Szeredi
2020-03-23 17:27         ` Amir Goldstein [this message]
2020-03-23 19:15           ` Amir Goldstein
2020-03-24  6:27             ` Amir Goldstein
2020-03-23 14:27 ` Miklos Szeredi

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