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Message-ID: <Y+LuG+mNwY46obat@rowland.harvard.edu>
Date: Tue, 7 Feb 2023 19:34:35 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
USB list <linux-usb@...r.kernel.org>,
Hillf Danton <hdanton@...a.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: Converting dev->mutex into dev->spinlock ?
On Wed, Feb 08, 2023 at 07:17:20AM +0900, Tetsuo Handa wrote:
> On 2023/02/08 2:46, Alan Stern wrote:
> > The real question is what will happen in your syzbot test scenarios.
> > Lockdep certainly ought to be able to detect a real deadlock when one
> > occurs. It will be more interesting to find out if it can warn about
> > potential deadlocks _without_ them occurring.
>
> For example, https://syzkaller.appspot.com/x/repro.c?x=15556074480000 generates
> below warning, but I don't have syzbot environment. Please propose an updated
> patch (which won't hit WARN_ON_ONCE()) for allowing people to try it in syzbot
> environment.
Here is a patch. I haven't tried to compile it.
Alan Stern
Index: usb-devel/drivers/base/core.c
===================================================================
--- usb-devel.orig/drivers/base/core.c
+++ usb-devel/drivers/base/core.c
@@ -2322,6 +2322,9 @@ static void device_release(struct kobjec
devres_release_all(dev);
kfree(dev->dma_range_map);
+ mutex_destroy(&dev->mutex);
+ if (!lockdep_static_obj(dev))
+ lockdep_unregister_key(&dev->mutex_key);
if (dev->release)
dev->release(dev);
@@ -2941,7 +2944,10 @@ void device_initialize(struct device *de
kobject_init(&dev->kobj, &device_ktype);
INIT_LIST_HEAD(&dev->dma_pools);
mutex_init(&dev->mutex);
- lockdep_set_novalidate_class(&dev->mutex);
+ if (!lockdep_static_obj(dev)) {
+ lockdep_register_key(&dev->mutex_key);
+ lockdep_set_class(&dev->mutex, &dev->mutex_key);
+ }
spin_lock_init(&dev->devres_lock);
INIT_LIST_HEAD(&dev->devres_head);
device_pm_init(dev);
Index: usb-devel/include/linux/device.h
===================================================================
--- usb-devel.orig/include/linux/device.h
+++ usb-devel/include/linux/device.h
@@ -570,6 +570,7 @@ struct device {
struct mutex mutex; /* mutex to synchronize calls to
* its driver.
*/
+ struct lock_class_key mutex_key; /* Unique key for each device */
struct dev_links_info links;
struct dev_pm_info power;
Index: usb-devel/include/linux/lockdep.h
===================================================================
--- usb-devel.orig/include/linux/lockdep.h
+++ usb-devel/include/linux/lockdep.h
@@ -172,6 +172,7 @@ do { \
current->lockdep_recursion -= LOCKDEP_OFF; \
} while (0)
+extern int lockdep_static_obj(const void *obj);
extern void lockdep_register_key(struct lock_class_key *key);
extern void lockdep_unregister_key(struct lock_class_key *key);
Index: usb-devel/kernel/locking/lockdep.c
===================================================================
--- usb-devel.orig/kernel/locking/lockdep.c
+++ usb-devel/kernel/locking/lockdep.c
@@ -831,7 +831,7 @@ static int arch_is_kernel_initmem_freed(
}
#endif
-static int static_obj(const void *obj)
+int lockdep_static_obj(const void *obj)
{
unsigned long start = (unsigned long) &_stext,
end = (unsigned long) &_end,
@@ -857,6 +857,7 @@ static int static_obj(const void *obj)
*/
return is_module_address(addr) || is_module_percpu_address(addr);
}
+EXPORT_SYMBOL_GPL(lockdep_static_obj);
#endif
/*
@@ -969,7 +970,7 @@ static bool assign_lock_key(struct lockd
lock->key = (void *)can_addr;
else if (__is_module_percpu_address(addr, &can_addr))
lock->key = (void *)can_addr;
- else if (static_obj(lock))
+ else if (lockdep_static_obj(lock))
lock->key = (void *)lock;
else {
/* Debug-check: all keys must be persistent! */
@@ -1220,7 +1221,7 @@ void lockdep_register_key(struct lock_cl
struct lock_class_key *k;
unsigned long flags;
- if (WARN_ON_ONCE(static_obj(key)))
+ if (WARN_ON_ONCE(lockdep_static_obj(key)))
return;
hash_head = keyhashentry(key);
@@ -1246,7 +1247,7 @@ static bool is_dynamic_key(const struct
struct lock_class_key *k;
bool found = false;
- if (WARN_ON_ONCE(static_obj(key)))
+ if (WARN_ON_ONCE(lockdep_static_obj(key)))
return false;
/*
@@ -1293,7 +1294,7 @@ register_lock_class(struct lockdep_map *
if (!lock->key) {
if (!assign_lock_key(lock))
return NULL;
- } else if (!static_obj(lock->key) && !is_dynamic_key(lock->key)) {
+ } else if (!lockdep_static_obj(lock->key) && !is_dynamic_key(lock->key)) {
return NULL;
}
@@ -4836,7 +4837,7 @@ void lockdep_init_map_type(struct lockde
* Sanity check, the lock-class key must either have been allocated
* statically or must have been registered as a dynamic key.
*/
- if (!static_obj(key) && !is_dynamic_key(key)) {
+ if (!lockdep_static_obj(key) && !is_dynamic_key(key)) {
if (debug_locks)
printk(KERN_ERR "BUG: key %px has not been registered!\n", key);
DEBUG_LOCKS_WARN_ON(1);
@@ -6335,7 +6336,7 @@ void lockdep_unregister_key(struct lock_
might_sleep();
- if (WARN_ON_ONCE(static_obj(key)))
+ if (WARN_ON_ONCE(lockdep_static_obj(key)))
return;
raw_local_irq_save(flags);
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