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kobject: delayed kobject release: help find buggy drivers

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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>
This commit is contained in:
Russell King 2013-06-27 15:06:14 +01:00 committed by Greg Kroah-Hartman
parent 7c42721fe0
commit c817a67ecb
3 changed files with 42 additions and 3 deletions
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4
include/linux/kobject.h
View File

@ -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;

19
lib/Kconfig.debug
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@ -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

22
lib/kobject.c
View File

@ -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
}
/**