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

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Date:   Wed, 18 Apr 2018 13:42:03 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     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>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Subject: Re: [RFC PATCH 31/35] Revert "vfs: add d_real_inode() helper"

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?
>
> 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.

Thanks,
Miklos