linux-kernel - Re: "fs/namei.c: keep track of nd->root refcount status" causes boot panic

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Message-ID: <20190903130456.GA9567@infradead.org>
Date:   Tue, 3 Sep 2019 06:04:56 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Qian Cai <cai@....pw>, linux-fsdevel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: "fs/namei.c: keep track of nd->root refcount status" causes boot
 panic

On Tue, Sep 03, 2019 at 01:37:19PM +0100, Al Viro wrote:
> On Tue, Sep 03, 2019 at 12:21:36AM -0400, Qian Cai wrote:
> > The linux-next commit "fs/namei.c: keep track of nd->root refcount status” [1] causes boot panic on all
> > architectures here on today’s linux-next (0902). Reverted it will fix the issue.
> 
> <swearing>
> 
> OK, I see what's going on.  Incremental to be folded in:
> 
> diff --git a/include/linux/namei.h b/include/linux/namei.h
> index 20ce2f917ef4..2ed0942a67f8 100644
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -20,8 +20,8 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
>  #define LOOKUP_FOLLOW		0x0001	/* follow links at the end */
>  #define LOOKUP_DIRECTORY	0x0002	/* require a directory */
>  #define LOOKUP_AUTOMOUNT	0x0004  /* force terminal automount */
> -#define LOOKUP_EMPTY		0x4000	/* accept empty path [user_... only] */
> -#define LOOKUP_DOWN		0x8000	/* follow mounts in the starting point */
> +#define LOOKUP_EMPTY		0x8000	/* accept empty path [user_... only] */
> +#define LOOKUP_DOWN		0x10000	/* follow mounts in the starting point */
>  
>  #define LOOKUP_REVAL		0x0020	/* tell ->d_revalidate() to trust no cache */
>  #define LOOKUP_RCU		0x0040	/* RCU pathwalk mode; semi-internal */

Any chance to keep these ordered numerically to avoid someone else
introdcing this kind of bug again later on?