linux-kernel - Re: [PATCH 6/7] fcntl: Don't use ambiguous SIG_POLL si

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Date:   Thu, 20 Jul 2017 18:16:04 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrei Vagin <avagin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>, Greg KH <greg@...ah.com>,
        Andrey Vagin <avagin@...nvz.org>,
        Serge Hallyn <serge@...lyn.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Willy Tarreau <w@....eu>, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH 6/7] fcntl: Don't use ambiguous SIG_POLL si_codes

On 07/18, Eric W. Biederman wrote:
>
> -			BUG_ON((reason & __SI_MASK) != __SI_POLL);
> +			BUG_ON((reason < POLL_IN) || (reason > NSIGPOLL));
                                                      ^^^^^^^^^^^^^^^^^
looks obviously wrong? Say, POLL_IN is obviously > NSIGPOLL == 6.

Probably you meant

			BUG_ON((reason < POLL_IN) || (reason - POLL_IN > NSIGPOLL)

?

but this contradicts with the next line:

>  			if (reason - POLL_IN >= NSIGPOLL)
>  				si.si_band  = ~0L;

confused...

Oleg.