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Message-Id: <201005312132.28631.rusty@rustcorp.com.au>
Date: Mon, 31 May 2010 21:32:27 +0930
From: Rusty Russell <rusty@...tcorp.com.au>
To: Brandon Philips <brandon@...p.org>
Cc: "Rafael J. Wysocki" <rjw@...k.pl>,
Linus Torvalds <torvalds@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Jon Masters <jonathan@...masters.org>,
Tejun Heo <htejun@...il.com>,
Masami Hiramatsu <mhiramat@...hat.com>,
Kay Sievers <kay.sievers@...y.org>
Subject: [PATCH 2/2] 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 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 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@...tcorp.com.au>
Cc: Brandon Philips <brandon@...p.org>
Cc: Avi Kivity <avi@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Tim Abbot <tabbott@...lice.com>
---
kernel/module.c | 91 ++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 59 insertions(+), 32 deletions(-)
diff --git a/kernel/module.c b/kernel/module.c
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -559,40 +559,33 @@ static int already_uses(struct module *a
}
/* 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)
{
struct module_use *use;
int no_warn, err;
- if (b == NULL || already_uses(a, b)) return 1;
+ if (b == NULL || already_uses(a, b))
+ return 0;
/* 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);
- return 0;
- }
-
- /* If strong_try_module_get() returned a different error, we fail. */
+ err = strong_try_module_get(b);
if (err)
- return 0;
+ return err;
DEBUGP("Allocating new usage for %s.\n", a->name);
use = kmalloc(sizeof(*use), GFP_ATOMIC);
if (!use) {
printk("%s: out of memory loading\n", a->name);
module_put(b);
- return 0;
+ return -ENOMEM;
}
use->module_which_uses = a;
list_add(&use->list, &b->modules_which_use_me);
no_warn = sysfs_create_link(b->holders_dir, &a->mkobj.kobj, a->name);
- 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)
@@ -888,11 +881,11 @@ static inline void module_unload_free(st
{
}
-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)
{
@@ -1057,26 +1050,58 @@ static inline int same_magic(const char
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@....net>
@@ -1578,21 +1603,23 @@ static int simplify_symbols(Elf_Shdr *se
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:
--
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