linux-kernel - Re: Regression with orderly

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Message-ID: <20130312182210.GA15862@redhat.com>
Date:	Tue, 12 Mar 2013 19:22:10 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Lucas De Marchi <lucas.de.marchi@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>, david@...son.dropbear.id.au,
	Kees Cook <keescook@...omium.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Feng Hong <hongfeng@...vell.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
Subject: Re: Regression with orderly_poweroff()

On 03/12, Lucas De Marchi wrote:
>
> I have some pending patches on LKML to remove
> call_usermodehelper_fns() and export call_usermodehelper_{setup,exec}.
>  Doing this we can separate the allocation part using GFP_ATOMIC

But this is pointless. Contrary, we should change __orderly_poweroff()
to do not use GFP_ATOMIC for argv_split(), see below.

> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2194,7 +2194,8 @@ static int __orderly_poweroff(void)
>   "PATH=/sbin:/bin:/usr/sbin:/usr/bin",
>   NULL
>   };
> - int ret;
> + struct subprocess_info *info;
> + int ret = -ENOMEM;
> 
>   argv = argv_split(GFP_ATOMIC, poweroff_cmd, &argc);
>   if (argv == NULL) {
> @@ -2203,7 +2204,10 @@ static int __orderly_poweroff(void)
>   return -ENOMEM;
>   }
> 
> - ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
> + info = call_usermodehelper_setup(argv[0], argv, envp, GFP_ATOMIC,
> + NULL, NULL, NULL);
> + if (info)
> + ret = call_usermodehelper_exec(info, UMH_WAIT_EXEC);

And how this can help? The real problem is not GFP_KERNEL.
call_usermodehelper_exec(UMH_WAIT_EXEC) will block.

Oleg.

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