linux-kernel - Re: [RFC] Suspicious bug in module refcounting

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Message-Id: <200902042125.48723.rusty@rustcorp.com.au>
Date:	Wed, 4 Feb 2009 21:25:47 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Russell King <rmk+lkml@....linux.org.uk>
Cc:	Karsten Keil <kkeil@...e.de>, linux-kernel@...r.kernel.org,
	Michal Hocko <mhocko@...e.cz>,
	richard kennedy <richard@....demon.co.uk>,
	Dan Williams <dan.j.williams@...el.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	dwmw2@...radead.org, Scott Wood <scottwood@...escale.com>,
	netdev@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC] Suspicious bug in module refcounting

On Wednesday 04 February 2009 20:41:30 Russell King wrote:
> On Wed, Feb 04, 2009 at 02:18:08PM +1030, Rusty Russell wrote:
> >   gameport.c, serio.c and input.c increment their own refcount, but to get
> > into those init functions someone must be holding a refcount already (ie. a
> > module depends on this module).  Ditto cyber2000fb.c, and MTD.
> 
> Err, wrong.  cyber2000fb.c does it in its module initialization function
> to prevent the module (when built for Shark) from being unloaded.  It
> does this because it's from the days of 2.2 kernels and no one bothered
> writing the module unload support for Shark.  I'm certainly not in a
> position to do that.

Thanks, here's the patch then:

Subject: cyber2000fb.c: use proper method for stopping unload if CONFIG_ARCH_SHARK

Russell explains the __module_get():
> cyber2000fb.c does it in its module initialization function
> to prevent the module (when built for Shark) from being unloaded.  It
> does this because it's from the days of 2.2 kernels and no one bothered
> writing the module unload support for Shark.

Since 2.4, the correct answer has been to not define an unload fn.

Cc: Russell King <rmk+lkml@....linux.org.uk>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

diff --git a/drivers/video/cyber2000fb.c b/drivers/video/cyber2000fb.c
--- a/drivers/video/cyber2000fb.c
+++ b/drivers/video/cyber2000fb.c
@@ -1736,10 +1736,8 @@ static int __init cyber2000fb_init(void)
 
 #ifdef CONFIG_ARCH_SHARK
 	err = cyberpro_vl_probe();
-	if (!err) {
+	if (!err)
 		ret = 0;
-		__module_get(THIS_MODULE);
-	}
 #endif
 #ifdef CONFIG_PCI
 	err = pci_register_driver(&cyberpro_driver);
@@ -1749,14 +1747,15 @@ static int __init cyber2000fb_init(void)
 
 	return ret ? err : 0;
 }
+module_init(cyber2000fb_init);
 
+#ifndef CONFIG_ARCH_SHARK
 static void __exit cyberpro_exit(void)
 {
 	pci_unregister_driver(&cyberpro_driver);
 }
-
-module_init(cyber2000fb_init);
 module_exit(cyberpro_exit);
+#endif
 
 MODULE_AUTHOR("Russell King");
 MODULE_DESCRIPTION("CyberPro 2000, 2010 and 5000 framebuffer driver");
--
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