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From: Rusty Russell on 20 Apr 2010 05:20
This fixes "gave up waiting for init of module libcrc32c." which
happened at boot time due to multiple parallel module loads.

The problem was a deadlock: we wait for a module to finish
initializing, but we keep the module_lock mutex so it can't complete.
In particular, this could reasonably happen if a module does a
request_module() in its initialization routine.

So we change use_module() to return an errno rather than a bool, and if
it's -EBUSY we drop the lock and wait in the caller, then reaquire the
lock.

Reported-by: Brandon Philips <brandon(a)ifup.org>
Signed-off-by: Rusty Russell <rusty(a)rustcorp.com.au>
Tested-by: Brandon Philips <brandon(a)ifup.org>
---
kernel/module.c | 57 +++++++++++++++++++++++++++++++++++---------------------
1 file changed, 36 insertions(+), 21 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -510,33 +510,26 @@ int use_module(struct module *a, struct
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);

@@ -823,7 +816,7 @@ static inline void module_unload_free(st

int use_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);

@@ -994,17 +987,39 @@ static const struct kernel_symbol *resol
struct module *owner;
const struct kernel_symbol *sym;
const unsigned long *crc;
+ DEFINE_WAIT(wait);
+ int err;
+ long timeleft = 30 * HZ;

+again:
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)
+ return NULL;
+
+ if (!check_version(sechdrs, versindex, name, mod, crc, owner))
+ return NULL;
+
+ prepare_to_wait(&module_wq, &wait, TASK_INTERRUPTIBLE);
+ err = use_module(mod, owner);
+ if (likely(!err) || err != -EBUSY || signal_pending(current)) {
+ finish_wait(&module_wq, &wait);
+ return err ? NULL : sym;
}
- return sym;
+
+ /* Module is still loading. Drop lock and wait. */
+ mutex_unlock(&module_mutex);
+ timeleft = schedule_timeout(timeleft);
+ mutex_lock(&module_mutex);
+ finish_wait(&module_wq, &wait);
+
+ /* Module might be gone entirely, or replaced. Re-lookup. */
+ if (timeleft)
+ goto again;
+
+ printk(KERN_WARNING "%s: gave up waiting for init of module %s.\n",
+ mod->name, owner->name);
+ return NULL;
}

/*
--
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Next: [PATCH] spi: spidev_test gives error upon 1-byte transfer