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

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Message-ID: <4B066F1F.7090902@gmail.com>
Date:	Fri, 20 Nov 2009 11:27:43 +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: acct_file_reopen() && do_acct_process() (Was: [PATCH 0/3] extend
 get/setrlimit to support setting rlimits external to a process (v7))

On 11/20/2009 03:11 AM, Oleg Nesterov wrote:
> Hmm. you are right. Do you know why acct_file_reopen() does
> 
> 	if (old_acct)
> 		do_acct_process();
> 
> ???
> 
> This looks just strange. What is the point ? If the caller doesn't
> exit, we shouldn't account it?

I have no idea. I just checked free and net bsds and they record only
exiting tasks. Maybe someone added it to record the process which
disabled the acct (last entry). Dunno.

> And this is just wrong, no? Even if we forget about rlim, since
> do_acct_process() does override_creds() + revert_creds(), any
> __task_cred() in between is fooled?
> 
> Probably I greatly misread something in acct.c, otherwise I can't
> see why, say, mntput() should ever record the caller in acct file.

>From how I understand the code, it is the last mntput before the fs gets
unmounted. It's to close the acct file. But I don't understand why it
accounts.

> IOW: could someone explain why the patch below is wrong?

For me, it makes sense. But that's not important ;).

> --- a/kernel/acct.c
> +++ b/kernel/acct.c
> @@ -206,7 +206,6 @@ static void acct_file_reopen(struct bsd_
>  	if (old_acct) {
>  		mnt_unpin(old_acct->f_path.mnt);
>  		spin_unlock(&acct_lock);
> -		do_acct_process(acct, old_ns, old_acct);
>  		filp_close(old_acct, NULL);
>  		spin_lock(&acct_lock);

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