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module: fix bne2 "gave up waiting for init of module libcrc32c" 

Problem: it's hard to avoid an init routine stumbling over a
request_module these days.  And it's not clear it's always a bad idea:
for example, a module like kvm with dynamic dependencies on kvm-intel
or kvm-amd would be neater if it could simply request_module the right
one.

In this particular case, it's libcrc32c:

	libcrc32c_mod_init
	 crypto_alloc_shash
	  crypto_alloc_tfm
	   crypto_find_alg
	    crypto_alg_mod_lookup
	     crypto_larval_lookup
	      request_module

If another module is waiting inside resolve_symbol() for libcrc32c to
finish initializing (ie. bne2 depends on libcrc32c) then it does so
holding the module lock, and our request_module() can't make progress
until that is released.

Waiting inside resolve_symbol() without the lock isn't all that hard:
we just need to pass the -EBUSY up the call chain so we can sleep
where we don't hold the lock.  Error reporting is a bit trickier: we
need to copy the name of the unfinished module before releasing the
lock.

Other notes:
1) This also fixes a theoretical issue where a weak dependency would allow
   symbol version mismatches to be ignored.
2) We rename use_module to ref_module to make life easier for the only
   external user (the out-of-tree ksplice patches).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tim Abbot <tabbott@ksplice.com>
Tested-by: Brandon Philips <bphilips@suse.de>
This commit is contained in:
Rusty Russell 2010-06-05 11:17:37 -06:00
parent be593f4ce4
commit 9bea7f2395
1 changed files with 59 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

91
kernel/module.c
View File

@ -582,33 +582,26 @@ static int add_module_usage(struct module *a, struct module *b)
}
/* Module a uses b: caller needs module_mutex() */
int use_module(struct module *a, struct module *b)
int ref_module(struct module *a, struct module *b)
{
int err;
if (b == NULL || already_uses(a, b)) return 1;
/* If we're interrupted or time out, we fail. */
if (wait_event_interruptible_timeout(
module_wq, (err = strong_try_module_get(b)) != -EBUSY,
30 * HZ) <= 0) {
printk("%s: gave up waiting for init of module %s.\n",
a->name, b->name);
if (b == NULL || already_uses(a, b))
return 0;
}
/* If strong_try_module_get() returned a different error, we fail. */
/* If module isn't available, we fail. */
err = strong_try_module_get(b);
if (err)
return 0;
return err;
err = add_module_usage(a, b);
if (err) {
module_put(b);
return 0;
return err;
}
return 1;
return 0;
}
EXPORT_SYMBOL_GPL(use_module);
EXPORT_SYMBOL_GPL(ref_module);
/* Clear the unload stuff of the module. */
static void module_unload_free(struct module *mod)
@ -893,11 +886,11 @@ static inline void module_unload_free(struct module *mod)
{
}
int use_module(struct module *a, struct module *b)
int ref_module(struct module *a, struct module *b)
{
return strong_try_module_get(b) == 0;
return strong_try_module_get(b);
}
EXPORT_SYMBOL_GPL(use_module);
EXPORT_SYMBOL_GPL(ref_module);
static inline void module_unload_init(struct module *mod)
{
@ -1062,26 +1055,58 @@ static inline int same_magic(const char *amagic, const char *bmagic,
static const struct kernel_symbol *resolve_symbol(Elf_Shdr *sechdrs,
unsigned int versindex,
const char *name,
struct module *mod)
struct module *mod,
char ownername[])
{
struct module *owner;
const struct kernel_symbol *sym;
const unsigned long *crc;
int err;
mutex_lock(&module_mutex);
sym = find_symbol(name, &owner, &crc,
!(mod->taints & (1 << TAINT_PROPRIETARY_MODULE)), true);
/* use_module can fail due to OOM,
or module initialization or unloading */
if (sym) {
if (!check_version(sechdrs, versindex, name, mod, crc, owner)
|| !use_module(mod, owner))
sym = NULL;
if (!sym)
goto unlock;
if (!check_version(sechdrs, versindex, name, mod, crc, owner)) {
sym = ERR_PTR(-EINVAL);
goto getname;
}
err = ref_module(mod, owner);
if (err) {
sym = ERR_PTR(err);
goto getname;
}
getname:
/* We must make copy under the lock if we failed to get ref. */
strncpy(ownername, module_name(owner), MODULE_NAME_LEN);
unlock:
mutex_unlock(&module_mutex);
return sym;
}
static const struct kernel_symbol *resolve_symbol_wait(Elf_Shdr *sechdrs,
unsigned int versindex,
const char *name,
struct module *mod)
{
const struct kernel_symbol *ksym;
char ownername[MODULE_NAME_LEN];
if (wait_event_interruptible_timeout(module_wq,
!IS_ERR(ksym = resolve_symbol(sechdrs, versindex, name,
mod, ownername)) ||
PTR_ERR(ksym) != -EBUSY,
30 * HZ) <= 0) {
printk(KERN_WARNING "%s: gave up waiting for init of module %s.\n",
mod->name, ownername);
}
return ksym;
}
/*
* /sys/module/foo/sections stuff
* J. Corbet <corbet@lwn.net>
@ -1638,21 +1663,23 @@ static int simplify_symbols(Elf_Shdr *sechdrs,
break;
case SHN_UNDEF:
ksym = resolve_symbol(sechdrs, versindex,
strtab + sym[i].st_name, mod);
ksym = resolve_symbol_wait(sechdrs, versindex,
strtab + sym[i].st_name,
mod);
/* Ok if resolved. */
if (ksym) {
if (ksym && !IS_ERR(ksym)) {
sym[i].st_value = ksym->value;
break;
}
/* Ok if weak. */
if (ELF_ST_BIND(sym[i].st_info) == STB_WEAK)
if (!ksym && ELF_ST_BIND(sym[i].st_info) == STB_WEAK)
break;
printk(KERN_WARNING "%s: Unknown symbol %s\n",
mod->name, strtab + sym[i].st_name);
ret = -ENOENT;
printk(KERN_WARNING "%s: Unknown symbol %s (err %li)\n",
mod->name, strtab + sym[i].st_name,
PTR_ERR(ksym));
ret = PTR_ERR(ksym) ?: -ENOENT;
break;
default: