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    Subject[PATCH tip/core/rcu 22/23] tree/tiny rcu: Add debug RCU head objects (v5)
    Date
    From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

    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>
    ---
    include/linux/rcupdate.h | 49 +++++++++++++++
    kernel/rcupdate.c | 149 ++++++++++++++++++++++++++++++++++++++++++++++
    kernel/rcutiny.c | 2 +
    kernel/rcutree.c | 2 +
    lib/Kconfig.debug | 6 ++
    5 files changed, 208 insertions(+), 0 deletions(-)

    diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    index 729cab8..f2bc463 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 */
    @@ -73,6 +74,16 @@ extern void rcu_init(void);
    #error "Unknown RCU implementation specified to kernel configuration"
    #endif

    +/*
    + * 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)
    {
    }
    @@ -80,6 +91,7 @@ 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

    @@ -502,4 +514,41 @@ 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 689281e..7780427 100644
    --- a/kernel/rcupdate.c
    +++ b/kernel/rcupdate.c
    @@ -103,3 +103,152 @@ void wakeme_after_rcu(struct rcu_head *head)
    rcu = container_of(head, struct rcu_synchronize, head);
    complete(&rcu->completion);
    }
    +
    +#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.
    + */
    +#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_init(head, &rcuhead_debug_descr);
    + return 1;
    +#endif
    + 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.
    + */
    +#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_activate(head, &rcuhead_debug_descr);
    + return 1;
    +#endif
    + 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;
    + }
    +}
    +
    +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);
    +
    +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 40d7be7..dd8e8d2 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
    + 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
    --
    1.7.0


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