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Date:   Mon, 27 Jul 2020 03:44:26 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Christoph Hellwig <hch@lst.de>,
        Lukasz Stelmach <l.stelmach@samsung.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Song Liu <song@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-raid@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Shaohua Li <shli@fb.com>
Subject: Re: [PATCH 16/23] initramfs: simplify clean_rootfs
Message-ID: <20200727024426.GI23808@casper.infradead.org>
References: <20200714190427.4332-1-hch@lst.de>
 <20200714190427.4332-17-hch@lst.de>
 <CGME20200717205549eucas1p13fca9a8496836faa71df515524743648@eucas1p1.samsung.com>
 <7f37802c-d8d9-18cd-7394-df51fa785988@samsung.com>
 <20200718100035.GA8856@lst.de>
 <20200723092200.GA19922@lst.de>
 <dleftjblk6b95t.fsf%l.stelmach@samsung.com>
 <20200723142734.GA11080@lst.de>
 <20200727024149.GB795125@ZenIV.linux.org.uk>
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On Mon, Jul 27, 2020 at 03:41:49AM +0100, Al Viro wrote:
> On Thu, Jul 23, 2020 at 04:27:34PM +0200, Christoph Hellwig wrote:
> > On Thu, Jul 23, 2020 at 04:25:34PM +0200, Lukasz Stelmach wrote:
> > > >> Can you comment out the call to d_genocide?  It seems like for your
> > > >> the fact that clean_rootfs didn't actually clean up was a feature and
> > > >> not a bug.
> > > >> 
> > > >> I guess the old, pre-2008 code also wouldn't have worked for you in
> > > >> that case.
> > > >
> > > > Did you get a chance to try this?
> > > 
> > > Indeed, commenting out d_genocide() helps.
> > 
> > So given that people have relied on at least the basic device nodes
> > like /dev/console to not go away since 2008, I wonder if we should just
> > remove clean_rootfs entirely
> > 
> > Linus, Al?
> 
> First of all, d_genocide() is simply wrong here from VFS point of view.  _IF_
> you want recursive removal, you need simple_recursive_remove(path.dentry, NULL).
> And it's a userland-visible change of behaviour.
> 
> As for removal of clean_rootfs()...  FWIW, the odds of an image that would
> eventually fail accidentally getting past the signature mismatch check are
> fairly low.  I've no idea what scenario the author of that thing used to have;
> that would be Shaohua Li <shaohua.li@intel.com>.  Cc'd...

Shaohua is now at Facebook.