linux-kernel - Re: [tip:core/signals] signals/sigaltstack: Prepare to add new SS

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Message-ID: <CALCETrV8BDqTpSisPLH=QYuEi0cSzZEX3gf9gO++Y3ioK3BzaQ@mail.gmail.com>
Date:	Tue, 3 May 2016 09:44:39 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Peter Zijlstra <peterz@...radead.org>,
	"Amanieu d'Antras" <amanieu@...il.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Shuah Khan <shuahkh@....samsung.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Richard Weinberger <richard@....at>,
	Brian Gerst <brgerst@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Stas Sergeev <stsp@...t.ru>, Al Viro <viro@...iv.linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>
Cc:	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:core/signals] signals/sigaltstack: Prepare to add new SS_xxx flags

On Tue, May 3, 2016 at 9:13 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, May 3, 2016 at 12:50 AM, tip-bot for Stas Sergeev
> <tipbot@...or.com> wrote:
>> Commit-ID:  407bc16ad1769f5cb8ad9555611cb198187ef4cd
>> Gitweb:     http://git.kernel.org/tip/407bc16ad1769f5cb8ad9555611cb198187ef4cd
>> Author:     Stas Sergeev <stsp@...t.ru>
>> AuthorDate: Thu, 14 Apr 2016 23:20:03 +0300
>> Committer:  Ingo Molnar <mingo@...nel.org>
>> CommitDate: Tue, 3 May 2016 08:37:59 +0200
>>
>> signals/sigaltstack: Prepare to add new SS_xxx flags
>>
>> This patch adds SS_FLAG_BITS - the mask that splits sigaltstack
>> mode values and bit-flags. Since there is no bit-flags yet, the
>> mask is defined to 0. The flags are added by subsequent patches.
>> With every new flag, the mask should have the appropriate bit cleared.
>>
>> This makes sure if some flag is tried on a kernel that doesn't
>> support it, the -EINVAL error will be returned, because such a
>> flag will be treated as an invalid mode rather than the bit-flag.
>>
>> That way the existence of the particular features can be probed
>> at run-time.
>>
>> This change was suggested by Andy Lutomirski:
>>
>>   https://lkml.org/lkml/2016/3/6/158
>
> LGTM.

Correction: does not LGTM.  In a sensible design, sigaltstack would
report flags back to the caller.  I will send a fix.

--Andy