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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Tue, 27 Nov 2018 11:33:33 +0100
Message-ID: <CAJfpeguWXT5w20tGeJ55CHBvp_3prYWKnxSPd3Osj3wXp68PMQ@mail.gmail.com>
Subject: Re: [PATCH V2] namei: free new_dentry late
To:     Jan Kara <jack@suse.cz>
Cc:     bianpan2016@163.com, Al Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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On Tue, Nov 27, 2018 at 11:05 AM Jan Kara <jack@suse.cz> wrote:
>
> On Tue 27-11-18 17:57:12, PanBian wrote:

> > I am not quite sure about the actual execution logic. But I guess new_dentry
> > reference may be dropped outside vfs_rename in cocurrent executions.
> > Otherwise, there is no need to acquire & drop new_dentry reference as it
> > is always alive along vfs_rename.
>
> I don't think that's the case. The dget() - dput() pair just looks
> superfluous to me in vfs_rename(). Am I missing something Miklos?

I think those are to protect against d_delete() called from fs to
reset d_inode.  The caller indeed has to hold one ref anyway.

So not superfluous, but only needed due to d_delete() and not to
protect against freeing of dentry.

Thanks,
Miklos