[PATCH] module_put_and_exit

Author: Neil Brown

Define module_put_and_exit() and use it for nfsd/lockd

Both nfsd and lockd have threads which expect to hold a reference
to the module while the thread is running.  In order for the thread
to be able to put_module() the module before exiting, the
put_module code must be call from outside the module.

This patch provides module_put_and_exit in non-modular code which a
thread-in-a-module can call.  It also gets nfsd and lockd to use it
as appropriate.

Note that in lockd, we can __get_module in the thread itself as the
creator of the thread is waiting for the thread to startup.

In nfsd and for the 'reclaimer' threaded started by locked, we
__get_module first and put_module if the thread failed to start.

fs/lockd/clntlock.c

@@ -187,8 +187,9 @@ nlmclnt_recovery(struct nlm_host *host, u32 newstate)
 	} else {
 		nlmclnt_prepare_reclaim(host, newstate);
 		nlm_get_host(host);
-		MOD_INC_USE_COUNT;
-		kernel_thread(reclaimer, host, CLONE_KERNEL);
+		__module_get(THIS_MODULE);
+		if (kernel_thread(reclaimer, host, CLONE_KERNEL))
+			module_put(THIS_MODULE);
 	}
 }
 
@@ -244,7 +245,5 @@ reclaimer(void *ptr)
 	nlm_release_host(host);
 	lockd_down();
 	unlock_kernel();
-	MOD_DEC_USE_COUNT;
-
-	return 0;
+	module_put_and_exit(0);
 }

fs/lockd/svc.c

@@ -88,7 +88,11 @@ lockd(struct svc_rqst *rqstp)
 	unsigned long grace_period_expire;
 
 	/* Lock module and set up kernel thread */
-	MOD_INC_USE_COUNT;
+	/* lockd_up is waiting for us to startup, so will
+	 * be holding a reference to this module, so it
+	 * is safe to just claim another reference
+	 */
+	__module_get(THIS_MODULE);
 	lock_kernel();
 
 	/*
@@ -183,7 +187,7 @@ lockd(struct svc_rqst *rqstp)
 
 	/* Release module */
 	unlock_kernel();
-	MOD_DEC_USE_COUNT;
+	module_put_and_exit(0);
 }
 
 /*

fs/nfsd/nfssvc.c

@@ -116,9 +116,12 @@ nfsd_svc(unsigned short port, int nrservs)
 	nrservs -= (nfsd_serv->sv_nrthreads-1);
 	while (nrservs > 0) {
 		nrservs--;
+		__module_get(THIS_MODULE);
 		error = svc_create_thread(nfsd, nfsd_serv);
-		if (error < 0)
+		if (error < 0) {
+			module_put(THIS_MODULE);
 			break;
+		}
 	}
 	victim = nfsd_list.next;
 	while (nrservs < 0 && victim != &nfsd_list) {
@@ -175,7 +178,6 @@ nfsd(struct svc_rqst *rqstp)
 	sigset_t shutdown_mask, allowed_mask;
 
 	/* Lock module and set up kernel thread */
-	MOD_INC_USE_COUNT;
 	lock_kernel();
 	daemonize("nfsd");
 	current->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
@@ -281,7 +283,7 @@ nfsd(struct svc_rqst *rqstp)
 	svc_exit_thread(rqstp);
 
 	/* Release module */
-	MOD_DEC_USE_COUNT;
+	module_put_and_exit(0);
 }
 
 int

include/linux/module.h

@@ -277,8 +277,12 @@ struct module *module_get_kallsym(unsigned int symnum,
 				  char *type,
 				  char namebuf[128]);
 int is_exported(const char *name, const struct module *mod);
-#ifdef CONFIG_MODULE_UNLOAD
 
+extern void __module_put_and_exit(struct module *mod, long code)
+	__attribute__((noreturn));
+#define module_put_and_exit(code) __module_put_and_exit(THIS_MODULE, code);
+
+#ifdef CONFIG_MODULE_UNLOAD
 unsigned int module_refcount(struct module *mod);
 void __symbol_put(const char *symbol);
 #define symbol_put(x) __symbol_put(MODULE_SYMBOL_PREFIX #x)
@@ -440,6 +444,8 @@ static inline int unregister_module_notifier(struct notifier_block * nb)
 	return 0;
 }
 
+#define module_put_and_exit(code) do_exit(code)
+
 #endif /* CONFIG_MODULES */
 
 #ifdef MODULE

kernel/module.c

@@ -98,6 +98,17 @@ int init_module(void)
 }
 EXPORT_SYMBOL(init_module);
 
+/* A thread that wants to hold a reference to a module only while it
+ * is running can call ths to safely exit.
+ * nfsd and lockd use this.
+ */
+void __module_put_and_exit(struct module *mod, long code)
+{
+	module_put(mod);
+	do_exit(code);
+}
+EXPORT_SYMBOL(__module_put_and_exit);
+	
 /* Find a module section: 0 means not found. */
 static unsigned int find_sec(Elf_Ehdr *hdr,
 			     Elf_Shdr *sechdrs,