Re: [PATCH v5 00/17] x86: Rewrite exit-to-userspace code

From: Andy Lutomirski <luto@amacapital.net>
To: Ingo Molnar <mingo@kernel.org>
Cc: "Andy Lutomirski" <luto@kernel.org>, "X86 ML" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Rik van Riel" <riel@redhat.com>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Denys Vlasenko" <vda.linux@googlemail.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Kees Cook" <keescook@chromium.org>,
	"Brian Gerst" <brgerst@gmail.com>,
	"Paul McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v5 00/17] x86: Rewrite exit-to-userspace code
Date: Tue, 7 Jul 2015 09:03:32 -0700	[thread overview]
Message-ID: <CALCETrX2dzef73rkSNppfSZ+GTTidN36QgzcnxxCbyPUgvyGtA@mail.gmail.com> (raw)
In-Reply-To: <20150707111234.GA13554@gmail.com>

On Tue, Jul 7, 2015 at 4:12 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> So this looks mostly problem free on my boxen, except this warning triggers:
>
> Adding 3911820k swap on /dev/sda2.  Priority:-1 extents:1 across:3911820k
> capability: warning: `dbus-daemon' uses 32-bit capabilities (legacy support in use)
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 2445 at arch/x86/entry/common.c:311 syscall_return_slowpath+0x4c/0x270()
> syscall 6 left IRQs disabled
> Modules linked in:
> CPU: 1 PID: 2445 Comm: distccd Not tainted 4.2.0-rc1-01597-gaecd781-dirty #18
>  0000000000000000 00000000776afac2 ffff880035413e58 ffffffff81c8915f
>  0000000000000000 ffff880035413eb0 ffff880035413e98 ffffffff810a8d82
>  ffff880035413e78 ffff880035413f58 0000000020020002 ffff880035410000
> Call Trace:
>  [<ffffffff81c8915f>] dump_stack+0x4f/0x7b
>  [<ffffffff810a8d82>] warn_slowpath_common+0xa2/0xc0
>  [<ffffffff810a8df5>] warn_slowpath_fmt+0x55/0x70
>  [<ffffffff81001ddc>] syscall_return_slowpath+0x4c/0x270
>  [<ffffffff81c96471>] int_ret_from_sys_call+0x25/0x9f
> ---[ end trace 083efc734e089d37 ]---
> device: 'vcs2': device_add
> PM: Adding info for No Bus:vcs2
> device: 'vcsa2': device_add
>
> with ancient user-space, running the attached .config.
>
> The system booted up fine otherwise. The warning corresponds to:
>
>         if (WARN(irqs_disabled(), "syscall %ld left IRQs disabled",
>                  regs->orig_ax))
>                 local_irq_enable();
>
> and this was just the regular startup of the distccd daemon during bootup, nothing
> particularly fancy.
>
> Note that 'distccd' is a 32-bit ELF binary - and this is a 64-bit kernel.
>
> Syscall 6 would be:
>
> arch/x86/entry/syscalls/syscall_32.tbl:6        i386    close                   sys_close
>
> Thanks,
>
>         Ingo

It's irq state confusion in these lovely macros:

#ifndef CONFIG_AUDITSYSCALL
# define sysexit_audit        ia32_ret_from_sys_call
# define sysretl_audit        ia32_ret_from_sys_call
#endif

Frankly, I'm amazed that the old code seems to have worked.  I should
have a patch for you later today.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC