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From: Miklos Szeredi <miklos@szeredi.hu>
To: Amir Goldstein <amir73il@gmail.com>
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 15:21:24 +0100
Message-ID: <CAJfpegtCn-HLhuDB98G4dO8L-t2PMcqcwDw+0TiknU5LGvBacQ@mail.gmail.com> (raw)
In-Reply-To: <CAOQ4uxiW2-Hh_sfuYXeuQy=a6FYBm7DyWkysgEe1GnC-qWWivg@mail.gmail.com>

On Mon, Mar 23, 2020 at 2:24 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Mon, Mar 23, 2020 at 2:53 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Mon, Mar 23, 2020 at 9:50 AM Phasip <phasip@gmail.com> wrote:
> > >
> > > Hello!
> > >
> > > I have stumbled upon two ways of producing kernel warnings when using the overlayfs, both seem to be results of the same issue.
> > >
> > > The issue seems to be related to handling of hard links that are created directly in the upperdir.
> > > Below is my system details and then two samples with a list of commands to reproduce and the corresponding kernel warning
> >
> > Hi,
> >
> > Thanks for the report.
> >
> > The problem is that i_nlink is not kept in sync with changes to
> > underlying layers.   That would not in itself be an issue, since
> > modification of the underlying layers may result in
> > undefined/unexpected behavior.  The problem is that this manifests
> > itself as a kernel warning.
> >
> > Since unlink/rename is synchronized on the victim inode (the one that
> > is getting removed) it is possible to detect this condition and
> > prevent drop_nlink() from being called.
> >
> > Attached patch fixes both of your testcases.
>
> 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.

> We better replace the WARN_ON() with pr_warn_ratelimited().
>
> >
> > We'll need an xfstests case for this as well.
> >
>
> Please forward the part of the email with the test case to the list.

Okay.

Thanks,
Miklos

  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 [this message]
2020-03-23 14:53       ` Miklos Szeredi
2020-03-23 17:27         ` Amir Goldstein
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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