Re: __unsafe() usage

Rusty Russell
2007-07-23T23:17:19Z

On Mon, 2007-07-23 at 19:59 +0200, Adrian Bunk wrote:
> On Mon, Jul 23, 2007 at 09:05:54AM -0700, Nelson, Shannon wrote:
> > Gabriel C [mailto:nix.or.die@googlemail.com]
> > >
> > >Hi,
> > >
> > >I got this warning on current git using gcc 4.2.1 :
> > >
> > >...
> > >
> > >drivers/dma/ioatdma.c: In function 'ioat_init_module':
> > >drivers/dma/ioatdma.c:816: warning: the address of
> > >'__this_module' will always evaluate as 'true'
> >...
>
> I'm less interested in why this gives a warning, more interesting is the
> code:
> __unsafe(THIS_MODULE);
>
> @Rusty:
> As far as I understand it, __unsafe() wasn't intended for such a usage,
> and simply not providing an exit function would be the right solution?
> If this is true, and since the MOD_INC_USE_COUNT compat code is long
> gone, shouldn't we be able to completely remove __unsafe() and the
> struct member "unsafe"?

Yes, indeed, something like this:
==
Remove "unsafe" from module struct

Adrian Bunk points out that "unsafe" was used to mark modules touched by
the deprecated MOD_INC_USE_COUNT interface, which has long gone. It's
time to remove the member from the module structure, as well.

If you want a module which can't unload, don't register an exit
function.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -r d7af727512fd drivers/dma/ioatdma.c
--- a/drivers/dma/ioatdma.c Tue Jul 24 08:30:05 2007 +1000
+++ b/drivers/dma/ioatdma.c Tue Jul 24 09:11:11 2007 +1000
@@ -811,18 +811,17 @@ MODULE_AUTHOR("Intel Corporation");

static int __init ioat_init_module(void)
{
- /* it's currently unsafe to unload this module */
- /* if forced, worst case is that rmmod hangs */
- __unsafe(THIS_MODULE);
-
return pci_register_driver(&ioat_pci_driver);
}

module_init(ioat_init_module);

+/* it's currently unsafe to unload this module */
+#if 0
static void __exit ioat_exit_module(void)
{
pci_unregister_driver(&ioat_pci_driver);
}

module_exit(ioat_exit_module);
+#endif
diff -r d7af727512fd drivers/dma/iop-adma.c
--- a/drivers/dma/iop-adma.c Tue Jul 24 08:30:05 2007 +1000
+++ b/drivers/dma/iop-adma.c Tue Jul 24 09:11:30 2007 +1000
@@ -1446,21 +1446,20 @@ static struct platform_driver iop_adma_d

static int __init iop_adma_init (void)
{
- /* it's currently unsafe to unload this module */
- /* if forced, worst case is that rmmod hangs */
- __unsafe(THIS_MODULE);
-
return platform_driver_register(&iop_adma_driver);
}

+/* it's currently unsafe to unload this module */
+#if 0
static void __exit iop_adma_exit (void)
{
platform_driver_unregister(&iop_adma_driver);
return;
}
+module_exit(iop_adma_exit);
+#endif

module_init(iop_adma_init);
-module_exit(iop_adma_exit);

MODULE_AUTHOR("Intel Corporation");
MODULE_DESCRIPTION("IOP ADMA Engine Driver");
diff -r d7af727512fd include/linux/module.h
--- a/include/linux/module.h Tue Jul 24 08:30:05 2007 +1000
+++ b/include/linux/module.h Tue Jul 24 09:00:19 2007 +1000
@@ -312,9 +312,6 @@ struct module
/* Arch-specific module values */
struct mod_arch_specific arch;

- /* Am I unsafe to unload? */
- int unsafe;
-
unsigned int taints; /* same bits as kernel:tainted */

#ifdef CONFIG_GENERIC_BUG
@@ -441,16 +438,6 @@ static inline void __module_get(struct m
__mod ? __mod->name : "kernel"; \
})

-#define __unsafe(mod) \
-do { \
- if (mod && !(mod)->unsafe) { \
- printk(KERN_WARNING \
- "Module %s cannot be unloaded due to unsafe usage in" \
- " %s:%u\n", (mod)->name, __FILE__, __LINE__); \
- (mod)->unsafe = 1; \
- } \
-} while(0)
-
/* For kallsyms to ask for address resolution. NULL means not found. */
const char *module_address_lookup(unsigned long addr,
unsigned long *symbolsize,
@@ -518,8 +505,6 @@ static inline void module_put(struct mod

#define module_name(mod) "kernel"

-#define __unsafe(mod)
-
/* For kallsyms to ask for address resolution. NULL means not found. */
static inline const char *module_address_lookup(unsigned long addr,
unsigned long *symbolsize,
diff -r d7af727512fd kernel/module.c
--- a/kernel/module.c Tue Jul 24 08:30:05 2007 +1000
+++ b/kernel/module.c Tue Jul 24 09:00:58 2007 +1000
@@ -692,8 +692,7 @@ sys_delete_module(const char __user *nam
}

/* If it has an init func, it must have an exit func to unload */
- if ((mod->init != NULL && mod->exit == NULL)
- || mod->unsafe) {
+ if (mod->init && !mod->exit) {
forced = try_force_unload(flags);
if (!forced) {
/* This module can't be removed */
@@ -739,11 +738,6 @@ static void print_unload_info(struct seq
list_for_each_entry(use, &mod->modules_which_use_me, list) {
printed_something = 1;
seq_printf(m, "%s,", use->module_which_uses->name);
- }
-
- if (mod->unsafe) {
- printed_something = 1;
- seq_printf(m, "[unsafe],");
}

if (mod->init != NULL && mod->exit == NULL) {
@@ -2012,15 +2006,10 @@ sys_init_module(void __user *umod,
buggy refcounters. */
mod->state = MODULE_STATE_GOING;
synchronize_sched();
- if (mod->unsafe)
- printk(KERN_ERR "%s: module is now stuck!\n",
- mod->name);
- else {
- module_put(mod);
- mutex_lock(&module_mutex);
- free_module(mod);
- mutex_unlock(&module_mutex);
- }
+ module_put(mod);
+ mutex_lock(&module_mutex);
+ free_module(mod);
+ mutex_unlock(&module_mutex);
return ret;
}

diff -r d7af727512fd net/sctp/protocol.c
--- a/net/sctp/protocol.c Tue Jul 24 08:30:05 2007 +1000
+++ b/net/sctp/protocol.c Tue Jul 24 09:12:43 2007 +1000
@@ -1176,7 +1176,6 @@ SCTP_STATIC __init int sctp_init(void)
if (status)
goto err_v6_add_protocol;

- __unsafe(THIS_MODULE);
status = 0;
out:
return status;
@@ -1216,6 +1215,7 @@ err_chunk_cachep:
goto out;
}

+#if 0
/* Exit handler for the SCTP protocol. */
SCTP_STATIC __exit void sctp_exit(void)
{
@@ -1263,9 +1263,10 @@ SCTP_STATIC __exit void sctp_exit(void)

proto_unregister(&sctp_prot);
}
+module_exit(sctp_exit);
+#endif

module_init(sctp_init);
-module_exit(sctp_exit);

/*
* __stringify doesn't likes enums, so use IPPROTO_SCTP value (132) directly.