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Commit 24da1cbf authored by Rusty Russell's avatar Rusty Russell Committed by Linus Torvalds
Browse files

modules: remove modlist_lock 



Now we always use stop_machine for module insertion or deletion, we no
longer need the modlist_lock: merely disabling preemption is sufficient to
block against list manipulation.  This avoids deadlock on OOPSen where we
can potentially grab the lock twice.

Bug: 8695
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Tobias Oed <tobiasoed@hotmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6c675bd4

kernel/module.c

+15 −21
Original line number Diff line number Diff line
@@ -61,10 +61,8 @@ extern int module_sysfs_initialized; 
/* If this is set, the section belongs in the init part of the module */

#define INIT_OFFSET_MASK (1UL << (BITS_PER_LONG-1))



/* Protects module list */

static DEFINE_SPINLOCK(modlist_lock);



/* List of modules, protected by module_mutex AND modlist_lock */

/* List of modules, protected by module_mutex or preempt_disable

 * (add/delete uses stop_machine). */

static DEFINE_MUTEX(module_mutex);

static LIST_HEAD(modules);
@@ -760,14 +758,13 @@ static void print_unload_info(struct seq_file *m, struct module *mod) 
void __symbol_put(const char *symbol)

{

	struct module *owner;

	unsigned long flags;

	const unsigned long *crc;



	spin_lock_irqsave(&modlist_lock, flags);

	preempt_disable();

	if (!__find_symbol(symbol, &owner, &crc, 1))

		BUG();

	module_put(owner);

	spin_unlock_irqrestore(&modlist_lock, flags);

	preempt_enable();

}

EXPORT_SYMBOL(__symbol_put);
@@ -1228,14 +1225,14 @@ static void free_module(struct module *mod) 
void *__symbol_get(const char *symbol)

{

	struct module *owner;

	unsigned long value, flags;

	unsigned long value;

	const unsigned long *crc;



	spin_lock_irqsave(&modlist_lock, flags);

	preempt_disable();

	value = __find_symbol(symbol, &owner, &crc, 1);

	if (value && !strong_try_module_get(owner))

		value = 0;

	spin_unlock_irqrestore(&modlist_lock, flags);

	preempt_enable();



	return (void *)value;

}
@@ -2308,11 +2305,10 @@ const struct seq_operations modules_op = { 
/* Given an address, look for it in the module exception tables. */

const struct exception_table_entry *search_module_extables(unsigned long addr)

{

	unsigned long flags;

	const struct exception_table_entry *e = NULL;

	struct module *mod;



	spin_lock_irqsave(&modlist_lock, flags);

	preempt_disable();

	list_for_each_entry(mod, &modules, list) {

		if (mod->num_exentries == 0)

			continue;
@@ -2323,7 +2319,7 @@ const struct exception_table_entry *search_module_extables(unsigned long addr) 
		if (e)

			break;

	}

	spin_unlock_irqrestore(&modlist_lock, flags);

	preempt_enable();



	/* Now, if we found one, we are running inside it now, hence

           we cannot unload the module, hence no refcnt needed. */
@@ -2335,25 +2331,24 @@ const struct exception_table_entry *search_module_extables(unsigned long addr) 
 */

int is_module_address(unsigned long addr)

{

	unsigned long flags;

	struct module *mod;



	spin_lock_irqsave(&modlist_lock, flags);

	preempt_disable();



	list_for_each_entry(mod, &modules, list) {

		if (within(addr, mod->module_core, mod->core_size)) {

			spin_unlock_irqrestore(&modlist_lock, flags);

			preempt_enable();

			return 1;

		}

	}



	spin_unlock_irqrestore(&modlist_lock, flags);

	preempt_enable();



	return 0;

}





/* Is this a valid kernel address?  We don't grab the lock: we are oopsing. */

/* Is this a valid kernel address? */

struct module *__module_text_address(unsigned long addr)

{

	struct module *mod;
@@ -2368,11 +2363,10 @@ struct module *__module_text_address(unsigned long addr) 
struct module *module_text_address(unsigned long addr)

{

	struct module *mod;

	unsigned long flags;



	spin_lock_irqsave(&modlist_lock, flags);

	preempt_disable();

	mod = __module_text_address(addr);

	spin_unlock_irqrestore(&modlist_lock, flags);

	preempt_enable();



	return mod;

}