linux-kernel - Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits external to a process (v7)

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Message-ID: <4B040A03.2020508@gmail.com>
Date:	Wed, 18 Nov 2009 15:51:47 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>, Neil Horman <nhorman@...driver.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	marcin.slusarz@...il.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits external
 to a process (v7)

On 11/09/2009 06:36 PM, Oleg Nesterov wrote:
> We can call find_task_by_vpid() under rcu and do get_task_struct().
> Or, given that we need tasklist anyway we can do find_task_by_vpid()
> under tasklist and do not get() at all.

Thanks. I'll post patches as a reply to this email. They are on the top
of the previous series which were already in -next. They're here (on the
same thread level):
http://lkml.org/lkml/2009/9/3/296

All patches available as:
git://decibel.fi.muni.cz/~xslaby/linux writable_limits-testing
or on web:
http://decibel.fi.muni.cz/cgi-bin/gitweb.cgi?p=linux.git;a=shortlog;h=refs/heads/writable_limits-testing

If somebody would like to pick them up, I have also a -next based
version (fanotify+recvmsg syscalls collision).

What I did with the Neil's patches:
- changed syscall bodies according to comments and
- added entries to syscall_table_32.S
- implemented compat syscalls
- cleaned up rlim usage in posix cpu timers. Note that cpu and
  rttime are not guaranteed (concurrent setrlimit set might
  be overwritten by the stores there).
- reviewed rlim usages all over the tree

On the last point: I added explicit ACCESS_ONCE all over there. If you
don't like I will trash it. The only remaining weird user is in
kernel/acct.c:
        /*
         * Accounting records are not subject to resource limits.
         */
        flim = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
        current->signal->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
        file->f_op->write(file, (char *)&ac,
                               sizeof(acct_t), &file->f_pos);
        current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;

It means that threads of the process with PACCT caps have unlimited file
size for a short while. If there is setrlimit in between, it gets wiped
out as well. I don't know what to do with that.

Please review.

thanks,
-- 
js
Faculty of Informatics, Masaryk University
Suse Labs, Novell
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