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authorRussell King <rmk+kernel@arm.linux.org.uk>2013-06-27 15:06:14 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-07-25 15:39:04 -0700
commitc817a67ecba7c3c2aaa104796d78f160af60920d (patch)
tree6c23ee30ef86aeebe0ff75d60881aa6561951c9a
parent7c42721fe0c58a848849b43ff558cf2fb86aa35a (diff)
kobject: delayed kobject release: help find buggy drivers
Implement debugging for kobject release functions. kobjects are reference counted, so the drop of the last reference to them is not predictable. However, the common case is for the last reference to be the kobject's removal from a subsystem, which results in the release function being immediately called. This can hide subtle bugs, which can occur when another thread holds a reference to the kobject at the same time that a kobject is removed. This results in the release method being delayed. In order to make these kinds of problems more visible, the following patch implements a delayed release; this has the effect that the release function will be out of order with respect to the removal of the kobject in the same manner that it would be if a reference was being held. This provides us with an easy way to allow driver writers to debug their drivers and fix otherwise hidden problems. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--include/linux/kobject.h4
-rw-r--r--lib/Kconfig.debug19
-rw-r--r--lib/kobject.c22
3 files changed, 42 insertions, 3 deletions
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 939b11268c8..de6dcbcc6ef 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -26,6 +26,7 @@
#include <linux/kernel.h>
#include <linux/wait.h>
#include <linux/atomic.h>
+#include <linux/workqueue.h>
#define UEVENT_HELPER_PATH_LEN 256
#define UEVENT_NUM_ENVP 32 /* number of env pointers */
@@ -65,6 +66,9 @@ struct kobject {
struct kobj_type *ktype;
struct sysfs_dirent *sd;
struct kref kref;
+#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
+ struct delayed_work release;
+#endif
unsigned int state_initialized:1;
unsigned int state_in_sysfs:1;
unsigned int state_add_uevent_sent:1;
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1501aa55322..444e1c12fea 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -981,6 +981,25 @@ config DEBUG_KOBJECT
If you say Y here, some extra kobject debugging messages will be sent
to the syslog.
+config DEBUG_KOBJECT_RELEASE
+ bool "kobject release debugging"
+ depends on DEBUG_KERNEL
+ help
+ kobjects are reference counted objects. This means that their
+ last reference count put is not predictable, and the kobject can
+ live on past the point at which a driver decides to drop it's
+ initial reference to the kobject gained on allocation. An
+ example of this would be a struct device which has just been
+ unregistered.
+
+ However, some buggy drivers assume that after such an operation,
+ the memory backing the kobject can be immediately freed. This
+ goes completely against the principles of a refcounted object.
+
+ If you say Y here, the kernel will delay the release of kobjects
+ on the last reference count to improve the visibility of this
+ kind of kobject release bug.
+
config HAVE_DEBUG_BUGVERBOSE
bool
diff --git a/lib/kobject.c b/lib/kobject.c
index 4a1f33d4354..1d46c151a4a 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -545,8 +545,8 @@ static void kobject_cleanup(struct kobject *kobj)
struct kobj_type *t = get_ktype(kobj);
const char *name = kobj->name;
- pr_debug("kobject: '%s' (%p): %s\n",
- kobject_name(kobj), kobj, __func__);
+ pr_debug("kobject: '%s' (%p): %s, parent %p\n",
+ kobject_name(kobj), kobj, __func__, kobj->parent);
if (t && !t->release)
pr_debug("kobject: '%s' (%p): does not have a release() "
@@ -580,9 +580,25 @@ static void kobject_cleanup(struct kobject *kobj)
}
}
+#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
+static void kobject_delayed_cleanup(struct work_struct *work)
+{
+ kobject_cleanup(container_of(to_delayed_work(work),
+ struct kobject, release));
+}
+#endif
+
static void kobject_release(struct kref *kref)
{
- kobject_cleanup(container_of(kref, struct kobject, kref));
+ struct kobject *kobj = container_of(kref, struct kobject, kref);
+#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
+ pr_debug("kobject: '%s' (%p): %s, parent %p (delayed)\n",
+ kobject_name(kobj), kobj, __func__, kobj->parent);
+ INIT_DELAYED_WORK(&kobj->release, kobject_delayed_cleanup);
+ schedule_delayed_work(&kobj->release, HZ);
+#else
+ kobject_cleanup(kobj);
+#endif
}
/**