linux-kernel - Re: [RFC PATCH 31/35] Revert "vfs: add d_real

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Date:   Wed, 18 Apr 2018 15:49:02 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Amir Goldstein <amir73il@...il.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Howard McLauchlan <hmclauchlan@...com>
Subject: Re: [RFC PATCH 31/35] Revert "vfs: add d_real_inode() helper"

On Wed, Apr 18, 2018 at 3:38 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Wed, 18 Apr 2018 13:42:03 +0200
> Miklos Szeredi <miklos@...redi.hu> wrote:
>
>> On Wed, Apr 18, 2018 at 10:19 AM, Amir Goldstein <amir73il@...il.com> wrote:
>> > On Thu, Apr 12, 2018 at 6:08 PM, Miklos Szeredi <mszeredi@...hat.com> wrote:
>> >> This reverts commit a118084432d642eeccb961c7c8cc61525a941fcb.
>> >>
>> >> No user of d_real_inode() remains, so it can be removed.
>> >>
>> >
>> > FYI, there is a new user in v4.17-rc1 added by commit
>> > f0a2aa5a2a40 tracing/uprobe: Add support for overlayfs
>> >
>> > Seems like this patch got merged without any CC to overlayfs
>> > mailing list nor maintainer?
>
> It appeared to be a small change with lots of reviewers. I didn't think
> it was something to notify the overlayfs folks with. But perhaps I was
> wrong.

The patch is correct.  The code surrounding it isn't, though.

>
>> >
>> > Not sure yet if overlayfs-rorw patches would allow reverting this
>> > change.
>>
>> Not trivial, because uprobe is looking at i_mapping to get a list of
>> current memory maps.   We could set i_mapping at overlay inode
>> initialization time, but we definitely can't *change* i_mapping at
>> copy up.  Which is bound to result in some weird inconsistencies.  So
>> likely we'll need to keep d_real_inode() for the time being.
>
> I just received this patch:
>
>  http://lkml.kernel.org/r/20180418062907.3210386-1-songliubraving@fb.com
>
> Which removes this code. Can you review it and I'll take it.

It shouldn't remove d_real_inode(), because that part is correct and
fixes a real bug in handling overlayfs files.

I'll review, but apparently I wasn't CC-d on that patch.   Weird.

Thanks,
Miklos