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authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>2010-04-17 08:48:42 -0400
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-06-14 16:37:26 -0700
commit551d55a944b143ef26fbd482d1c463199d6f65cf (patch)
tree6911d3f8e8719ba5ca43c83acdf87cbc8276d7d1
parent875352c94224c88f5aa28cb77206f993bd31b7a2 (diff)
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tree/tiny rcu: Add debug RCU head objects
Helps finding racy users of call_rcu(), which results in hangs because list entries are overwritten and/or skipped. Changelog since v4: - Bissectability is now OK - Now generate a WARN_ON_ONCE() for non-initialized rcu_head passed to call_rcu(). Statically initialized objects are detected with object_is_static(). - Rename rcu_head_init_on_stack to init_rcu_head_on_stack. - Remove init_rcu_head() completely. Changelog since v3: - Include comments from Lai Jiangshan This new patch version is based on the debugobjects with the newly introduced "active state" tracker. Non-initialized entries are all considered as "statically initialized". An activation fixup (triggered by call_rcu()) takes care of performing the debug object initialization without issuing any warning. Since we cannot increase the size of struct rcu_head, I don't see much room to put an identifier for statically initialized rcu_head structures. So for now, we have to live without "activation without explicit init" detection. But the main purpose of this debug option is to detect double-activations (double call_rcu() use of a rcu_head before the callback is executed), which is correctly addressed here. This also detects potential internal RCU callback corruption, which would cause the callbacks to be executed twice. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> CC: David S. Miller <davem@davemloft.net> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> CC: akpm@linux-foundation.org CC: mingo@elte.hu CC: laijs@cn.fujitsu.com CC: dipankar@in.ibm.com CC: josh@joshtriplett.org CC: dvhltc@us.ibm.com CC: niv@us.ibm.com CC: tglx@linutronix.de CC: peterz@infradead.org CC: rostedt@goodmis.org CC: Valdis.Kletnieks@vt.edu CC: dhowells@redhat.com CC: eric.dumazet@gmail.com CC: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
-rw-r--r--include/linux/rcupdate.h49
-rw-r--r--kernel/rcupdate.c160
-rw-r--r--kernel/rcutiny.c2
-rw-r--r--kernel/rcutree.c2
-rw-r--r--lib/Kconfig.debug6
5 files changed, 219 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b653b4a..2b7fc50 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -40,6 +40,7 @@
#include <linux/seqlock.h>
#include <linux/lockdep.h>
#include <linux/completion.h>
+#include <linux/debugobjects.h>
#ifdef CONFIG_RCU_TORTURE_TEST
extern int rcutorture_runnable; /* for sysctl */
@@ -79,6 +80,16 @@ extern void rcu_init(void);
(ptr)->next = NULL; (ptr)->func = NULL; \
} while (0)
+/*
+ * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
+ * initialization and destruction of rcu_head on the stack. rcu_head structures
+ * allocated dynamically in the heap or defined statically don't need any
+ * initialization.
+ */
+#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
+extern void init_rcu_head_on_stack(struct rcu_head *head);
+extern void destroy_rcu_head_on_stack(struct rcu_head *head);
+#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
static inline void init_rcu_head_on_stack(struct rcu_head *head)
{
}
@@ -86,6 +97,7 @@ static inline void init_rcu_head_on_stack(struct rcu_head *head)
static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
{
}
+#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -517,4 +529,41 @@ extern void call_rcu(struct rcu_head *head,
extern void call_rcu_bh(struct rcu_head *head,
void (*func)(struct rcu_head *head));
+/*
+ * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
+ * by call_rcu() and rcu callback execution, and are therefore not part of the
+ * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
+ */
+
+#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
+# define STATE_RCU_HEAD_READY 0
+# define STATE_RCU_HEAD_QUEUED 1
+
+extern struct debug_obj_descr rcuhead_debug_descr;
+
+static inline void debug_rcu_head_queue(struct rcu_head *head)
+{
+ debug_object_activate(head, &rcuhead_debug_descr);
+ debug_object_active_state(head, &rcuhead_debug_descr,
+ STATE_RCU_HEAD_READY,
+ STATE_RCU_HEAD_QUEUED);
+}
+
+static inline void debug_rcu_head_unqueue(struct rcu_head *head)
+{
+ debug_object_active_state(head, &rcuhead_debug_descr,
+ STATE_RCU_HEAD_QUEUED,
+ STATE_RCU_HEAD_READY);
+ debug_object_deactivate(head, &rcuhead_debug_descr);
+}
+#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
+static inline void debug_rcu_head_queue(struct rcu_head *head)
+{
+}
+
+static inline void debug_rcu_head_unqueue(struct rcu_head *head)
+{
+}
+#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
+
#endif /* __LINUX_RCUPDATE_H */
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 72a8dc9..4d16983 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -114,3 +114,163 @@ int rcu_my_thread_group_empty(void)
}
EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
#endif /* #ifdef CONFIG_PROVE_RCU */
+
+#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
+static inline void debug_init_rcu_head(struct rcu_head *head)
+{
+ debug_object_init(head, &rcuhead_debug_descr);
+}
+
+static inline void debug_rcu_head_free(struct rcu_head *head)
+{
+ debug_object_free(head, &rcuhead_debug_descr);
+}
+
+/*
+ * fixup_init is called when:
+ * - an active object is initialized
+ */
+static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
+{
+ struct rcu_head *head = addr;
+
+ switch (state) {
+ case ODEBUG_STATE_ACTIVE:
+ /*
+ * Ensure that queued callbacks are all executed.
+ * If we detect that we are nested in a RCU read-side critical
+ * section, we should simply fail, otherwise we would deadlock.
+ */
+ if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
+ irqs_disabled()) {
+ WARN_ON(1);
+ return 0;
+ }
+ rcu_barrier();
+ rcu_barrier_sched();
+ rcu_barrier_bh();
+ debug_object_init(head, &rcuhead_debug_descr);
+ return 1;
+ default:
+ return 0;
+ }
+}
+
+/*
+ * fixup_activate is called when:
+ * - an active object is activated
+ * - an unknown object is activated (might be a statically initialized object)
+ * Activation is performed internally by call_rcu().
+ */
+static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
+{
+ struct rcu_head *head = addr;
+
+ switch (state) {
+
+ case ODEBUG_STATE_NOTAVAILABLE:
+ /*
+ * This is not really a fixup. We just make sure that it is
+ * tracked in the object tracker.
+ */
+ debug_object_init(head, &rcuhead_debug_descr);
+ debug_object_activate(head, &rcuhead_debug_descr);
+ return 0;
+
+ case ODEBUG_STATE_ACTIVE:
+ /*
+ * Ensure that queued callbacks are all executed.
+ * If we detect that we are nested in a RCU read-side critical
+ * section, we should simply fail, otherwise we would deadlock.
+ */
+ if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
+ irqs_disabled()) {
+ WARN_ON(1);
+ return 0;
+ }
+ rcu_barrier();
+ rcu_barrier_sched();
+ rcu_barrier_bh();
+ debug_object_activate(head, &rcuhead_debug_descr);
+ return 1;
+ default:
+ return 0;
+ }
+}
+
+/*
+ * fixup_free is called when:
+ * - an active object is freed
+ */
+static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
+{
+ struct rcu_head *head = addr;
+
+ switch (state) {
+ case ODEBUG_STATE_ACTIVE:
+ /*
+ * Ensure that queued callbacks are all executed.
+ * If we detect that we are nested in a RCU read-side critical
+ * section, we should simply fail, otherwise we would deadlock.
+ */
+#ifndef CONFIG_PREEMPT
+ WARN_ON(1);
+ return 0;
+#else
+ if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
+ irqs_disabled()) {
+ WARN_ON(1);
+ return 0;
+ }
+ rcu_barrier();
+ rcu_barrier_sched();
+ rcu_barrier_bh();
+ debug_object_free(head, &rcuhead_debug_descr);
+ return 1;
+#endif
+ default:
+ return 0;
+ }
+}
+
+/**
+ * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
+ * @head: pointer to rcu_head structure to be initialized
+ *
+ * This function informs debugobjects of a new rcu_head structure that
+ * has been allocated as an auto variable on the stack. This function
+ * is not required for rcu_head structures that are statically defined or
+ * that are dynamically allocated on the heap. This function has no
+ * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
+ */
+void init_rcu_head_on_stack(struct rcu_head *head)
+{
+ debug_object_init_on_stack(head, &rcuhead_debug_descr);
+}
+EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
+
+/**
+ * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
+ * @head: pointer to rcu_head structure to be initialized
+ *
+ * This function informs debugobjects that an on-stack rcu_head structure
+ * is about to go out of scope. As with init_rcu_head_on_stack(), this
+ * function is not required for rcu_head structures that are statically
+ * defined or that are dynamically allocated on the heap. Also as with
+ * init_rcu_head_on_stack(), this function has no effect for
+ * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
+ */
+void destroy_rcu_head_on_stack(struct rcu_head *head)
+{
+ debug_object_free(head, &rcuhead_debug_descr);
+}
+EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
+
+struct debug_obj_descr rcuhead_debug_descr = {
+ .name = "rcu_head",
+ .fixup_init = rcuhead_fixup_init,
+ .fixup_activate = rcuhead_fixup_activate,
+ .fixup_free = rcuhead_fixup_free,
+};
+EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
+#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 38729d3..196ec02 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -169,6 +169,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
while (list) {
next = list->next;
prefetch(next);
+ debug_rcu_head_unqueue(list);
list->func(list);
list = next;
}
@@ -211,6 +212,7 @@ static void __call_rcu(struct rcu_head *head,
{
unsigned long flags;
+ debug_rcu_head_queue(head);
head->func = func;
head->next = NULL;
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d443734..d5bc439 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1112,6 +1112,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
while (list) {
next = list->next;
prefetch(next);
+ debug_rcu_head_unqueue(list);
list->func(list);
list = next;
if (++count >= rdp->blimit)
@@ -1388,6 +1389,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
unsigned long flags;
struct rcu_data *rdp;
+ debug_rcu_head_queue(head);
head->func = func;
head->next = NULL;
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e722e9d..142faa2 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -307,6 +307,12 @@ config DEBUG_OBJECTS_WORK
work queue routines to track the life time of work objects and
validate the work operations.
+config DEBUG_OBJECTS_RCU_HEAD
+ bool "Debug RCU callbacks objects"
+ depends on DEBUG_OBJECTS && PREEMPT
+ help
+ Enable this to turn on debugging of RCU list heads (call_rcu() usage).
+
config DEBUG_OBJECTS_ENABLE_DEFAULT
int "debug_objects bootup default value (0-1)"
range 0 1