linux-kernel - Re: [GIT] writable

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Message-ID: <AANLkTimPS_WFvEwyx+odwof5_AF5ZTOhu-3uK6m_VhYa@mail.gmail.com>
Date:	Tue, 10 Aug 2010 09:01:46 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jiri Slaby <jslaby@...e.cz>, Chris Metcalf <cmetcalf@...era.com>,
	Arnd Bergmann <arnd@...db.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT] writable_limits for 2.6.36

2010/8/7 Jiri Slaby <jslaby@...e.cz>:
>
> please consider the following repository for 2.6.36. It introduces a new
> syscall for arch independent resource limits handling. It also adds a
> support for runtime limits changing. This feature is needed mostly by
> daemons servicing databases and similar service where limits are needed
> to be changed without services being restarted on production systems.

Ok, so the code looks fine, and I don't have any real objections any
more. I don't know how much use this will get, but it doesn't appear
to be "wrong" in any way. So I was going to pull it.

However, in the meantime we have commit 5360bd776f73 ("Fix up the
"generic" unistd.h ABI to be more useful") that clashes with it. Now,
the conflict is trivial to resolve, and I could do that easily - it's
not a technical problem. But that commit code comments say

  + * Architectures may provide up to 16 syscalls of their own
  + * starting with this value.
  + */
  +#define __NR_arch_specific_syscall 244

and the new writable rlimits syscall is obviously 244.

Now, looking at it all, I think that commit was badly done - not
leaving any room for new generic system calls is pretty iffy. And if I
had happened to take the Tilera merge later, I'd have had no problems
with just changing it. As is, though, I want to check with Arnd and
Chris first.

Arnd, Chris - how about making the "arch-specific" system calls start
at 256 or something? Or even higher, like 512? Yes, it makes the
system call array bigger, but is that really a problem? Especially as
we start the "deprecated" system calls at 1024, it would seem to make
sense to raise it to 512, and leave the low numbers for the "regular"
system calls.

[ I'm leaving the quoted email for the edification of Chris/Arnd that
I added to the discussion ]

                                   Linus

---
>
>  git://decibel.fi.muni.cz/~xslaby/linux writable_limits
>
> Jiri Slaby (10):
>      rlimits: security, add task_struct to setrlimit
>      rlimits: add task_struct to update_rlimit_cpu
>      rlimits: split sys_setrlimit
>      rlimits: allow setrlimit to non-current tasks
>      rlimits: do security check under task_lock
>      rlimits: add rlimit64 structure
>      rlimits: redo do_setrlimit to more generic do_prlimit
>      rlimits: switch more rlimit syscalls to do_prlimit
>      rlimits: implement prlimit64 syscall
>      unistd: add __NR_prlimit64 syscall numbers
>
> Oleg Nesterov (2):
>      rlimits: make sure ->rlim_max never grows in sys_setrlimit
>      rlimits: selinux, do rlimits changes under task_lock
>
>  arch/x86/ia32/ia32entry.S          |    1 +
>  arch/x86/include/asm/unistd_32.h   |    3 +-
>  arch/x86/include/asm/unistd_64.h   |    2 +
>  arch/x86/kernel/syscall_table_32.S |    1 +
>  include/asm-generic/unistd.h       |    4 +-
>  include/linux/posix-timers.h       |    2 +-
>  include/linux/resource.h           |    9 ++
>  include/linux/security.h           |    9 +-
>  include/linux/syscalls.h           |    4 +
>  kernel/compat.c                    |   17 +---
>  kernel/posix-cpu-timers.c          |    8 +-
>  kernel/sys.c                       |  202 ++++++++++++++++++++++++++++--------
>  security/capability.c              |    3 +-
>  security/security.c                |    5 +-
>  security/selinux/hooks.c           |   12 ++-
>  15 files changed, 207 insertions(+), 75 deletions(-)
>
> thanks,
> --
> js
> suse labs
>
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