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Message-Id: <1285160840-16506-1-git-send-email-andi@firstfloor.org>
Date: Wed, 22 Sep 2010 15:07:20 +0200
From: Andi Kleen <andi@...stfloor.org>
To: linux-kernel@...r.kernel.org
Cc: Andi Kleen <ak@...ux.intel.com>, paulmck@...ux.vnet.ibm.com,
rusty@...tcorp.com.au, tglx@...utronix.de
Subject: [PATCH] Convert preempt_disabled in module.c to rcu read lock
From: Andi Kleen <ak@...ux.intel.com>
Thomas Gleixner pointed out that the list_for_each_rcu()
in module really need to use RCU read lock, not preempt disable.
This is especially needed for the preemptive RCU code.
>From what I understand the only reason for the preemption
disabling is to protect against rcu, so using rcu_read_lock()
is correct.
Open: this will do rcu_read_lock() asynchronously in oopses. That's ok
with all RCU implementations without deadlocks?
Cc: paulmck@...ux.vnet.ibm.com
Cc: rusty@...tcorp.com.au
Cc: tglx@...utronix.de
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
kernel/module.c | 78 ++++++++++++++++++++++++++----------------------------
1 files changed, 38 insertions(+), 40 deletions(-)
diff --git a/kernel/module.c b/kernel/module.c
index d0b5f8d..ea99f4c 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -74,7 +74,7 @@
/*
* Mutex protects:
- * 1) List of modules (also safely readable with preempt_disable),
+ * 1) List of modules (also safely readable with rcu_read_lock),
* 2) module_use links,
* 3) module_addr_min/module_addr_max.
* (delete uses stop_machine/add uses RCU list operations). */
@@ -344,7 +344,7 @@ static bool find_symbol_in_section(const struct symsearch *syms,
}
/* Find a symbol and return it, along with, (optional) crc and
- * (optional) module which owns it. Needs preempt disabled or module_mutex. */
+ * (optional) module which owns it. Needs rcu_read_lock or module_mutex. */
const struct kernel_symbol *find_symbol(const char *name,
struct module **owner,
const unsigned long **crc,
@@ -443,8 +443,7 @@ bool is_module_percpu_address(unsigned long addr)
struct module *mod;
unsigned int cpu;
- preempt_disable();
-
+ rcu_read_lock();
list_for_each_entry_rcu(mod, &modules, list) {
if (!mod->percpu_size)
continue;
@@ -453,13 +452,13 @@ bool is_module_percpu_address(unsigned long addr)
if ((void *)addr >= start &&
(void *)addr < start + mod->percpu_size) {
- preempt_enable();
+ rcu_read_unlock();
return true;
}
}
}
- preempt_enable();
+ rcu_read_unlock();
return false;
}
@@ -831,11 +830,11 @@ void __symbol_put(const char *symbol)
{
struct module *owner;
- preempt_disable();
+ rcu_read_lock();
if (!find_symbol(symbol, &owner, NULL, true, false))
BUG();
module_put(owner);
- preempt_enable();
+ rcu_read_unlock();
}
EXPORT_SYMBOL(__symbol_put);
@@ -870,7 +869,7 @@ static struct module_attribute refcnt = {
void module_put(struct module *module)
{
if (module) {
- preempt_disable();
+ rcu_read_lock();
smp_wmb(); /* see comment in module_refcount */
__this_cpu_inc(module->refptr->decs);
@@ -878,7 +877,7 @@ void module_put(struct module *module)
/* Maybe they're waiting for us to drop reference? */
if (unlikely(!module_is_live(module)))
wake_up_process(module->waiter);
- preempt_enable();
+ rcu_read_unlock();
}
}
EXPORT_SYMBOL(module_put);
@@ -1584,11 +1583,11 @@ void *__symbol_get(const char *symbol)
struct module *owner;
const struct kernel_symbol *sym;
- preempt_disable();
+ rcu_read_lock();
sym = find_symbol(symbol, &owner, NULL, true, true);
if (sym && strong_try_module_get(owner))
sym = NULL;
- preempt_enable();
+ rcu_read_unlock();
return sym ? (void *)sym->value : NULL;
}
@@ -2813,7 +2812,7 @@ static const char *get_ksymbol(struct module *mod,
}
/* For kallsyms to ask for address resolution. NULL means not found. Careful
- * not to lock to avoid deadlock on oopses, simply disable preemption. */
+ * not to lock to avoid deadlock on oopses, simply use rcu read lock. */
const char *module_address_lookup(unsigned long addr,
unsigned long *size,
unsigned long *offset,
@@ -2823,7 +2822,7 @@ const char *module_address_lookup(unsigned long addr,
struct module *mod;
const char *ret = NULL;
- preempt_disable();
+ rcu_read_lock();
list_for_each_entry_rcu(mod, &modules, list) {
if (within_module_init(addr, mod) ||
within_module_core(addr, mod)) {
@@ -2834,11 +2833,12 @@ const char *module_address_lookup(unsigned long addr,
}
}
/* Make a copy in here where it's safe */
+ /* AK: The string copy is likely racy. */
if (ret) {
strncpy(namebuf, ret, KSYM_NAME_LEN - 1);
ret = namebuf;
}
- preempt_enable();
+ rcu_read_unlock();
return ret;
}
@@ -2846,7 +2846,7 @@ int lookup_module_symbol_name(unsigned long addr, char *symname)
{
struct module *mod;
- preempt_disable();
+ rcu_read_lock();
list_for_each_entry_rcu(mod, &modules, list) {
if (within_module_init(addr, mod) ||
within_module_core(addr, mod)) {
@@ -2854,14 +2854,13 @@ int lookup_module_symbol_name(unsigned long addr, char *symname)
sym = get_ksymbol(mod, addr, NULL, NULL);
if (!sym)
- goto out;
+ break;
strlcpy(symname, sym, KSYM_NAME_LEN);
- preempt_enable();
+ rcu_read_unlock();
return 0;
}
}
-out:
- preempt_enable();
+ rcu_read_unlock();
return -ERANGE;
}
@@ -2870,7 +2869,7 @@ int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size,
{
struct module *mod;
- preempt_disable();
+ rcu_read_lock();
list_for_each_entry_rcu(mod, &modules, list) {
if (within_module_init(addr, mod) ||
within_module_core(addr, mod)) {
@@ -2878,17 +2877,16 @@ int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size,
sym = get_ksymbol(mod, addr, size, offset);
if (!sym)
- goto out;
+ break;
if (modname)
strlcpy(modname, mod->name, MODULE_NAME_LEN);
if (name)
strlcpy(name, sym, KSYM_NAME_LEN);
- preempt_enable();
+ rcu_read_unlock();
return 0;
}
}
-out:
- preempt_enable();
+ rcu_read_unlock();
return -ERANGE;
}
@@ -2897,7 +2895,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
{
struct module *mod;
- preempt_disable();
+ rcu_read_lock();
list_for_each_entry_rcu(mod, &modules, list) {
if (symnum < mod->num_symtab) {
*value = mod->symtab[symnum].st_value;
@@ -2906,12 +2904,12 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
KSYM_NAME_LEN);
strlcpy(module_name, mod->name, MODULE_NAME_LEN);
*exported = is_exported(name, *value, mod);
- preempt_enable();
+ rcu_read_unlock();
return 0;
}
symnum -= mod->num_symtab;
}
- preempt_enable();
+ rcu_read_unlock();
return -ERANGE;
}
@@ -2934,7 +2932,7 @@ unsigned long module_kallsyms_lookup_name(const char *name)
unsigned long ret = 0;
/* Don't lock: we're in enough trouble already. */
- preempt_disable();
+ rcu_read_lock();
if ((colon = strchr(name, ':')) != NULL) {
*colon = '\0';
if ((mod = find_module(name)) != NULL)
@@ -2945,7 +2943,7 @@ unsigned long module_kallsyms_lookup_name(const char *name)
if ((ret = mod_find_symname(mod, name)) != 0)
break;
}
- preempt_enable();
+ rcu_read_unlock();
return ret;
}
@@ -3083,7 +3081,7 @@ const struct exception_table_entry *search_module_extables(unsigned long addr)
const struct exception_table_entry *e = NULL;
struct module *mod;
- preempt_disable();
+ rcu_read_lock();
list_for_each_entry_rcu(mod, &modules, list) {
if (mod->num_exentries == 0)
continue;
@@ -3094,7 +3092,7 @@ const struct exception_table_entry *search_module_extables(unsigned long addr)
if (e)
break;
}
- preempt_enable();
+ rcu_read_unlock();
/* Now, if we found one, we are running inside it now, hence
we cannot unload the module, hence no refcnt needed. */
@@ -3112,9 +3110,9 @@ bool is_module_address(unsigned long addr)
{
bool ret;
- preempt_disable();
+ rcu_read_lock();
ret = __module_address(addr) != NULL;
- preempt_enable();
+ rcu_read_unlock();
return ret;
}
@@ -3153,9 +3151,9 @@ bool is_module_text_address(unsigned long addr)
{
bool ret;
- preempt_disable();
+ rcu_read_lock();
ret = __module_text_address(addr) != NULL;
- preempt_enable();
+ rcu_read_unlock();
return ret;
}
@@ -3164,7 +3162,7 @@ bool is_module_text_address(unsigned long addr)
* __module_text_address - get the module whose code contains an address.
* @addr: the address.
*
- * Must be called with preempt disabled or module mutex held so that
+ * Must be called with rcu read lock or module mutex held so that
* module doesn't get freed during this.
*/
struct module *__module_text_address(unsigned long addr)
@@ -3187,11 +3185,11 @@ void print_modules(void)
char buf[8];
printk(KERN_DEFAULT "Modules linked in:");
- /* Most callers should already have preempt disabled, but make sure */
- preempt_disable();
+ /* Most callers should already have rcu read lock but make sure */
+ rcu_read_lock();
list_for_each_entry_rcu(mod, &modules, list)
printk(" %s%s", mod->name, module_flags(mod, buf));
- preempt_enable();
+ rcu_read_unlock();
if (last_unloaded_module[0])
printk(" [last unloaded: %s]", last_unloaded_module);
printk("\n");
--
1.7.1
--
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