linux-kernel - Re: [PATCH 0/9] Refactoring exit

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Date:   Mon, 28 Jun 2021 11:20:03 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Michael Schmitz <schmitzmic@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Oleg Nesterov <oleg@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        alpha <linux-alpha@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Arnd Bergmann <arnd@...nel.org>, Tejun Heo <tj@...nel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 0/9] Refactoring exit

Geert Uytterhoeven <geert@...ux-m68k.org> writes:

> Hi Michael,
>
> On Mon, Jun 28, 2021 at 1:00 AM Michael Schmitz <schmitzmic@...il.com> wrote:
>> On 28/06/21 10:13 am, Al Viro wrote:
>> > On Thu, Jun 24, 2021 at 10:45:23PM +0000, Al Viro wrote:
>> >
>> >> 13) there's bdflush(1, whatever), which is equivalent to exit(0).
>> >> IMO it's long past the time to simply remove the sucker.
>> > Incidentally, calling that from ptraced process on alpha leads to
>> > the same headache for tracer.  _If_ we leave it around, this is
>> > another candidate for "hit yourself with that special signal" -
>> > both alpha and m68k have that syscall, and IMO adding an asm
>> > wrapper for that one is over the top.
>> >
>> > Said that, we really ought to bury that thing:
>> >
>> > commit 2f268ee88abb33968501a44368db55c63adaad40
>> > Author: Andrew Morton <akpm@...eo.com>
>> > Date:   Sat Dec 14 03:16:29 2002 -0800
>> >
>> >      [PATCH] deprecate use of bdflush()
>> >
>> >      Patch from Robert Love <rml@...h9.net>
>> >
>> >      We can never get rid of it if we do not deprecate it - so do so and
>> >      print a stern warning to those who still run bdflush daemons.
>> >
>> > Deprecated for 18.5 years by now - I seriously suspect that we have
>> > some contributors younger than that...
>>
>> Haven't found that warning in over 7 years' worth of console logs, and
>> I'm a good candidate for running the oldest userland in existence for m68k.
>>
>> Time to let it go.
>
> The warning is printed when using filesys-ELF-2.0.x-1400K-2.gz,
> which is a very old ramdisk from right after the m68k a.out to ELF
> transition:
>
>     warning: process `update' used the obsolete bdflush system call
>     Fix your initscripts?
>
> I still boot it, once in a while.

The only thing left in bdflush is func == 1 calls do_exit(0);

Which is a hack introduced in 2.3.23 aka October of 1999 to force the
userspace process calling bdflush to exit, instead of repeatedly calling
sys_bdflush.

Can you try deleting that func == 1 call and seeing if your old ramdisk
works?

I suspect userspace used to get into a tight spin calling bdflush
func == 1, when that function stopped doing anything.  That was back in
1999 so we are probably safe with out it.

Eric