linux-kernel - Re: [PATCH] usermodehelper: Fix -ENOMEM return logic

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Date:	Wed, 6 Mar 2013 23:05:12 -0300
From:	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
	James Morris <james.l.morris@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] usermodehelper: Fix -ENOMEM return logic

Hi Oleg,

On Mon, Feb 25, 2013 at 3:08 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 02/25, Lucas De Marchi wrote:
>>
>> Yep. The current interface is confusing. I agree that a separate
>> setup() + exec() would make more sense.
>
> Great,
>
>> > @@ -98,8 +98,14 @@ static int call_modprobe(char *module_na
>> >         argv[3] = module_name;  /* check free_modprobe_argv() */
>> >         argv[4] = NULL;
>> >
>> > -       return call_usermodehelper_fns(modprobe_path, argv, envp,
>> > -               wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
>> > +       info = call_usermodehelper_setup(...); // better name, please...
>> > +       if (!info)
>> > +               goto free_modname;
>> > +
>> > +       return call_usermodehelper_exec(info, wait);
>>
>> I'd say that in these cases the "call_" prefix has no meaning, and we
>> could just use a "usermodehelper" as the namespace.
>
> Oh, I agree with any naming.
>
> So, I hope you will send v2. I'd suggest to split the fixes. 1/3
> should create/export the new helpers, and 2-3 fix should call_modprobe()
> and call_usermodehelper_keys(). But this is up to you, I won't insist.

I was implementing this today, but looking into call_modprobe(), it is
never called with UMH_NO_WAIT. Doesn't it mean we can use a similar
trick as you used in __orderly_poweroff()? Then something similar to
this would be sufficient in this case (whitespace damaged):

diff --git a/kernel/kmod.c b/kernel/kmod.c
index b39f240..e4d6f6f 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -69,12 +69,6 @@ static DECLARE_RWSEM(umhelper_sem);
 */
 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";

-static void free_modprobe_argv(struct subprocess_info *info)
-{
-	kfree(info->argv[3]); /* check call_modprobe() */
-	kfree(info->argv);
-}
-
 static int call_modprobe(char *module_name, int wait)
 {
 	static char *envp[] = {
@@ -83,6 +77,7 @@ static int call_modprobe(char *module_name, int wait)
 		"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
 		NULL
 	};
+	int ret = -ENOMEM;

 	char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
 	if (!argv)
@@ -98,12 +93,13 @@ static int call_modprobe(char *module_name, int wait)
 	argv[3] = module_name;	/* check free_modprobe_argv() */
 	argv[4] = NULL;

-	return call_usermodehelper_fns(modprobe_path, argv, envp,
-		wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
+	ret = call_usermodehelper(modprobe_path, argv, envp,
+				  wait | UMH_KILLABLE);
+	kfree(module_name);
 free_argv:
 	kfree(argv);
 out:
-	return -ENOMEM;
+	return ret;
 }

 /**


Lucas De Marchi
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