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Date:   Sat, 14 Sep 2019 18:01:46 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     "zhengbin (A)" <zhengbin13@huawei.com>, Jan Kara <jack@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        "zhangyi (F)" <yi.zhang@huawei.com>, renxudong1@huawei.com,
        Hou Tao <houtao1@huawei.com>
Subject: Re: [PATCH] Re: Possible FS race condition between iterate_dir and
 d_alloc_parallel
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On Sat, Sep 14, 2019 at 09:49:21AM -0700, Linus Torvalds wrote:
> On Sat, Sep 14, 2019 at 9:16 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> >         OK, folks, could you try the following?  It survives the local beating
> > so far.
> 
> This looks like the right solution to me. Keep the locking simple,
> take the dentry refcount as long as we keep a ref to it in "*res".
> 
> However, the one thing that strikes me is that it looks to me like
> this means that the "cursor" and the dentry in "*res" are basically
> synonymous. Could we drop the cursor entirely, and just keep the ref
> to the last dentry we showd _as_ the cursor?

I thought of that, but AFAICS rename(2) is a fatal problem for such
a scheme.