From c817a67ecba7c3c2aaa104796d78f160af60920d Mon Sep 17 00:00:00 2001 From: Russell King Date: Thu, 27 Jun 2013 15:06:14 +0100 Subject: 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 Signed-off-by: Greg Kroah-Hartman --- lib/Kconfig.debug | 19 +++++++++++++++++++ lib/kobject.c | 22 +++++++++++++++++++--- 2 files changed, 38 insertions(+), 3 deletions(-) (limited to 'lib') 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 } /** -- cgit v1.2.3-18-g5258 From bd8c154a62d47b0ec2abf87e35dccf081781d81c Mon Sep 17 00:00:00 2001 From: "jbaron@akamai.com" Date: Tue, 27 Aug 2013 16:50:03 +0000 Subject: dynamic debug: line queries failing due to uninitialized local variable Settings of the form, 'line x module y +p', can fail arbitrarily due to an uninitialized local variable. With this patch results are consistent, as expected. Signed-off-by: Jason Baron Signed-off-by: Greg Kroah-Hartman --- lib/dynamic_debug.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'lib') diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c index 99fec3ae405..c37aeacd765 100644 --- a/lib/dynamic_debug.c +++ b/lib/dynamic_debug.c @@ -309,7 +309,7 @@ static int ddebug_parse_query(char *words[], int nwords, struct ddebug_query *query, const char *modname) { unsigned int i; - int rc; + int rc = 0; /* check we have an even number of words */ if (nwords % 2 != 0) { -- cgit v1.2.3-18-g5258