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SubjectRe: Locking Between User Context and Soft IRQs in 2.4.0
Keith Owens wrote:
>
> Pressed enter too soon.
>
> /*
> * Call device private open method
> */
>
> ret = -ENODEV;
> if (dev->open && try_inc_mod_count(dev->owner)) {
> if ((ret = dev->open(dev)) && dev->owner)
> __MOD_DEC_USE_COUNT(dev->owner);
> }

y'know, if we keep working this patch for about a year we
might end up getting it right. Thousand monkeys and all that.

The above assumes that (dev->open == 0) is an error, but
netdevices are in fact allowed to have a NULL open() method.

So hereunder is about the seventieth version of the netdevice
modules safety patch. Go wild.

Some notes:

- I've created the generic macro SET_OWNER_MODULE and put it
into modules.h. It may perhaps be useful for things other
than netdevices? The intent here is that 2.4-only drivers
can use:

SET_OWNER_MODULE(dev);

in their init routines.

Drivers which retain 2.2 compatibility should use:

#if LINUX_VERSION_CODE < KERNEL_VERSION(2,4,0)
#define SET_OWNER_MODULE(d)
#else
#undef MOD_INC_USE_COUNT
#undef MOD_DEC_USE_COUNT
#endif

xxx_probe()
{
...
SET_MODULE_OWNER(dev); /* 2.4 */
...
MOD_INC_USE_COUNT; /* 2.2 */
}

And everything should work.

- With this patch applied, the module refcounts for netdevices
will show doubled values in `lsmod', unless those drivers
have been changed to remove the now unneeded MOD_INC/DEC_USE_COUNT
macros (perhaps with the above 2.2-compatibility thing).



--- linux-2.4.0-test10/include/linux/netdevice.h Sat Nov 4 16:22:49 2000
+++ linux-akpm/include/linux/netdevice.h Sun Nov 5 22:15:48 2000
@@ -383,6 +383,9 @@
int (*neigh_setup)(struct net_device *dev, struct neigh_parms *);
int (*accept_fastpath)(struct net_device *, struct dst_entry*);

+ /* open/release and usage marking */
+ struct module *owner;
+
/* bridge stuff */
struct net_bridge_port *br_port;

--- linux-2.4.0-test10/include/linux/module.h Sat Nov 4 16:22:49 2000
+++ linux-akpm/include/linux/module.h Sun Nov 5 22:18:16 2000
@@ -313,4 +313,10 @@
#define EXPORT_NO_SYMBOLS
#endif /* MODULE */

+#ifdef CONFIG_MODULES
+#define SET_OWNER_MODULE(some_struct) do { some_struct->owner = THIS_MODULE; } while (0)
+#else
+#define SET_OWNER_MODULE(some_struct) do { } while (0)
+#endif
+
#endif /* _LINUX_MODULE_H */
--- linux-2.4.0-test10/net/core/dev.c Sat Nov 4 16:22:50 2000
+++ linux-akpm/net/core/dev.c Sun Nov 5 22:31:57 2000
@@ -93,6 +93,7 @@
#include <net/profile.h>
#include <linux/init.h>
#include <linux/kmod.h>
+#include <linux/module.h>
#if defined(CONFIG_NET_RADIO) || defined(CONFIG_NET_PCMCIA_RADIO)
#include <linux/wireless.h> /* Note : will define WIRELESS_EXT */
#endif /* CONFIG_NET_RADIO || CONFIG_NET_PCMCIA_RADIO */
@@ -666,9 +667,15 @@
/*
* Call device private open method
*/
-
- if (dev->open)
- ret = dev->open(dev);
+ if (try_inc_mod_count(dev->owner)) {
+ if (dev->open) {
+ ret = dev->open(dev);
+ if (ret != 0 && dev->owner)
+ __MOD_DEC_USE_COUNT(dev->owner);
+ }
+ } else {
+ ret = -ENODEV;
+ }

/*
* If it went open OK then:
@@ -783,6 +790,12 @@
* Tell people we are down
*/
notifier_call_chain(&netdev_chain, NETDEV_DOWN, dev);
+
+ /*
+ * Drop the module refcount
+ */
+ if (dev->owner)
+ __MOD_DEC_USE_COUNT(dev->owner);

return(0);
}
-
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