linux-kernel - Re: WARNING in notify

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Date:   Thu, 18 Apr 2019 13:03:56 +0200
From:   Jan Kara <jack@...e.cz>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Khazhismel Kumykov <khazhy@...gle.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        syzbot <syzbot+2b74da47f048a5046135@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org
Subject: Re: WARNING in notify_change

On Tue 16-04-19 00:54:28, Al Viro wrote:
> On Mon, Apr 15, 2019 at 04:20:17PM -0700, Khazhismel Kumykov wrote:
> > I was able to reproduce this by setting security.capability xattr on a
> > blockdev file, then writing to it - when writing to the blockdev we
> > never lock the inode, so when we clear the capability we hit this
> > lockdep warning.
> > 
> > Is the issue here that we can set this xattr in the first place so we
> > have to clear it at all? Or should we really be locking the inode for
> > blockdevs after all? I'm not too familiar, but my gut says former
> 
> More interesting question is, WTF do we even touch that thing for
> bdev?  The thing is, mknod will cheerfully create any number of
> different filesystem objects, all giving access to the same block
> device.  Which of them should have that xattr removed?  It makes
> no sense whatsoever; moreover, who *cares* about caps for block
> device in the first place?
> 
> And if we did, what of another way to modify the block device?
> You know, mount it read-write...

Yes, Alexander Lochman has sent a patch to silence this warning back in
February [1] by just bailing out from file_remove_privs() for non-regular
files.  But so far you've ignored that patch... Will you pick it up please?

								Honza

[1] https://lore.kernel.org/lkml/cbdc8071-de76-bb0a-6890-15ef21023a70@tu-dortmund.de

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR