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SubjectRe: Locking Between User Context and Soft IRQs in 2.4.0
Andrew Morton wrote:
>
> Perhaps the best thing to do here is to create a system-wide
> semaphore for module unloading. So we do a down()/up()
> in sys_delete_module() and do this in dev_open:

Yep. I think this is right. Jeff, this supersedes the
patch you sent to devem yesterday.


--- 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 12:40:00 2000
@@ -146,6 +146,11 @@
struct neigh_parms;
struct sk_buff;

+/* Centralised module refcounting for netdevices */
+struct module;
+#define SET_NETDEVICE_OWNER(dev) \
+ do { dev->owner = THIS_MODULE; } while (0)
+
struct netif_rx_stats
{
unsigned total;
@@ -382,6 +387,9 @@
unsigned char *haddr);
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 12:37:54 2000
@@ -146,10 +146,16 @@
#ifdef CONFIG_MODULES
extern unsigned long get_module_symbol(char *, char *);
extern void put_module_symbol(unsigned long);
+struct semaphore;
+extern struct semaphore mod_unload_sem;
+#define DOWN_MOD_UNLOAD_SEM() down(&mod_unload_sem)
+#define UP_MOD_UNLOAD_SEM() up(&mod_unload_sem)
#else
static inline unsigned long get_module_symbol(char *unused1, char *unused2) { return 0; };
static inline void put_module_symbol(unsigned long unused) { };
-#endif
+#define DOWN_MOD_UNLOAD_SEM() do { } while (0)
+#define UP_MOD_UNLOAD_SEM() do { } while (0)
+#endif

extern int try_inc_mod_count(struct module *mod);

--- 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 12:39:23 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 +667,20 @@
/*
* Call device private open method
*/
-
- if (dev->open)
- ret = dev->open(dev);
+ DOWN_MOD_UNLOAD_SEM(); /* Synchronise with sys_delete_module */
+ if (dev->owner == 0) {
+ if (dev->open)
+ ret = dev->open(dev);
+ } else {
+ if (try_inc_mod_count(dev->owner)) {
+ if (dev->open) {
+ if ((ret = dev->open(dev)) != 0)
+ __MOD_DEC_USE_COUNT(dev->owner);
+ }
+ } else
+ ret = -ENODEV;
+ }
+ UP_MOD_UNLOAD_SEM();

/*
* If it went open OK then:
@@ -783,6 +795,13 @@
* 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);
}
--- linux-2.4.0-test10/kernel/module.c Sat Nov 4 16:22:49 2000
+++ linux-akpm/kernel/module.c Sun Nov 5 12:36:03 2000
@@ -44,6 +44,7 @@
static struct module *find_module(const char *name);
static void free_module(struct module *, int tag_freed);

+DECLARE_MUTEX(mod_unload_sem);

/*
* Called at boot time
@@ -369,6 +370,7 @@
return -EPERM;

lock_kernel();
+ down(&mod_unload_sem);
if (name_user) {
if ((error = get_mod_name(name_user, &name)) < 0)
goto out;
@@ -431,6 +433,7 @@
mod->flags &= ~MOD_JUST_FREED;
error = 0;
out:
+ up(&mod_unload_sem);
unlock_kernel();
return error;
}
-
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