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Date:   Fri, 25 Jun 2021 17:58:36 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Justin He <Justin.He@arm.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
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Subject: Re: [PATCH 13/14] d_path: prepend_path() is unlikely to return
 non-zero
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On Fri, Jun 25, 2021 at 08:00:49AM +0000, Justin He wrote:
> --- a/fs/d_path.c
> +++ b/fs/d_path.c
> @@ -210,6 +210,7 @@ static int prepend_path(const struct path *path,
>         b = *p;
>         read_seqbegin_or_lock(&rename_lock, &seq);
>         error = __prepend_path(path->dentry, real_mount(path->mnt), root, &b);
> +       printk("prepend=%d",error);
>         if (!(seq & 1))
>                 rcu_read_unlock();
>         if (need_seqretry(&rename_lock, seq)) {
> 
> Then the result seems a little different:
> root@entos-ampere-02:~# dmesg |grep prepend=1 |wc -l
> 7417
> root@entos-ampere-02:~# dmesg |grep prepend=0 |wc -l
> 772
> 
> The kernel is 5.13.0-rc2+ + this series + my '%pD' series
> 
> Any thoughts?

On which loads?  1 here is "mount/dentry pair is in somebody
else's namespace or outside of the subtree we are chrooted
into".  IOW, what's calling d_path() on your setup?