On Mon, 2020-05-11 at 11:05 -0700, Paul E. McKenney wrote: > On Mon, May 11, 2020 at 10:31:11AM +0800, Walter Wu wrote: > > This feature will record first and last call_rcu() call stack and > > print two call_rcu() call stack in KASAN report. > > Suppose that a given rcu_head structure is passed to call_rcu(), then > the grace period elapses, the callback is invoked, and the enclosing > data structure is freed. But then that same region of memory is > immediately reallocated as the same type of structure and again > passed to call_rcu(), and that this cycle repeats several times. > > Would the first call stack forever be associated with the first > call_rcu() in this series? If so, wouldn't the last two usually > be the most useful? Or am I unclear on the use case? > The first call stack doesn't forever associate with first call_rcu(), if someone object freed and reallocated, then the first call stack will replace with new object. > > When call_rcu() is called, we store the call_rcu() call stack into > > slub alloc meta-data, so that KASAN report can print rcu stack. > > > > It doesn't increase the cost of memory consumption. Because we don't > > enlarge struct kasan_alloc_meta size. > > - add two call_rcu() call stack into kasan_alloc_meta, size is 8 bytes. > > - remove free track from kasan_alloc_meta, size is 8 bytes. > > > > [1]https://bugzilla.kernel.org/show_bug.cgi?id=198437 > > [2]https://groups.google.com/forum/#!searchin/kasan-dev/better$20stack$20traces$20for$20rcu%7Csort:date/kasan-dev/KQsjT_88hDE/7rNUZprRBgAJ > > > > Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx> > > Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> > > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > > Cc: Alexander Potapenko <glider@xxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Paul E. McKenney <paulmck@xxxxxxxxxx> > > Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx> > > Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> > > Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx> > > Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> > > --- > > include/linux/kasan.h | 2 ++ > > kernel/rcu/tree.c | 3 +++ > > lib/Kconfig.kasan | 2 ++ > > mm/kasan/common.c | 4 ++-- > > mm/kasan/generic.c | 29 +++++++++++++++++++++++++++++ > > mm/kasan/kasan.h | 19 +++++++++++++++++++ > > mm/kasan/report.c | 21 +++++++++++++++++---- > > 7 files changed, 74 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/kasan.h b/include/linux/kasan.h > > index 31314ca7c635..23b7ee00572d 100644 > > --- a/include/linux/kasan.h > > +++ b/include/linux/kasan.h > > @@ -174,11 +174,13 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; } > > > > void kasan_cache_shrink(struct kmem_cache *cache); > > void kasan_cache_shutdown(struct kmem_cache *cache); > > +void kasan_record_aux_stack(void *ptr); > > > > #else /* CONFIG_KASAN_GENERIC */ > > > > static inline void kasan_cache_shrink(struct kmem_cache *cache) {} > > static inline void kasan_cache_shutdown(struct kmem_cache *cache) {} > > +static inline void kasan_record_aux_stack(void *ptr) {} > > > > #endif /* CONFIG_KASAN_GENERIC */ > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 06548e2ebb72..de872b6cc261 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -57,6 +57,7 @@ > > #include <linux/slab.h> > > #include <linux/sched/isolation.h> > > #include <linux/sched/clock.h> > > +#include <linux/kasan.h> > > #include "../time/tick-internal.h" > > > > #include "tree.h" > > @@ -2694,6 +2695,8 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) > > trace_rcu_callback(rcu_state.name, head, > > rcu_segcblist_n_cbs(&rdp->cblist)); > > > > + kasan_record_aux_stack(head); > > Just for the record, at this point we have not yet queued the callback. > We have also not yet disabled interrupts. Which might be OK, but I > figured I should call out the possibility of moving this down a few > lines to follow the local_irq_save(). > We will intend to do it. > If someone incorrectly invokes concurrently invokes call_rcu() on this > same region of memory, possibly from an interrupt handler, we are OK > corrupting the stack traces, right? > Yes, and the wrong invoking call_rcu should be recorded. > But what happens if a given structure has more than one rcu_head > structure? In that case, RCU would be just fine with it being > concurrently passed to different call_rcu() invocations as long as the > two invocations didn't both use the same rcu_head structure. (In that > case, they had best not be both freeing the object, and if even one of > them is freeing the object, coordination is necessary.) > > If this is a problem, one approach would be to move the > kasan_record_aux_stack(head) call to kfree_rcu(). After all, it is > definitely illegal to pass the same memory to a pair of kfree_rcu() > invocations! ;-) > The function of kasan_record_aux_stack(head) is simple, it is only to record call stack by the 'head' object. Thanks. > Thanx, Paul > > > + > > /* Go handle any RCU core processing required. */ > > if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > > unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) { > > diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan > > index 81f5464ea9e1..56a89291f1cc 100644 > > --- a/lib/Kconfig.kasan > > +++ b/lib/Kconfig.kasan > > @@ -58,6 +58,8 @@ config KASAN_GENERIC > > For better error detection enable CONFIG_STACKTRACE. > > Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB > > (the resulting kernel does not boot). > > + Currently CONFIG_KASAN_GENERIC will print first and last call_rcu() > > + call stack. It doesn't increase the cost of memory consumption. > > > > config KASAN_SW_TAGS > > bool "Software tag-based mode" > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > > index 2906358e42f0..8bc618289bb1 100644 > > --- a/mm/kasan/common.c > > +++ b/mm/kasan/common.c > > @@ -41,7 +41,7 @@ > > #include "kasan.h" > > #include "../slab.h" > > > > -static inline depot_stack_handle_t save_stack(gfp_t flags) > > +depot_stack_handle_t kasan_save_stack(gfp_t flags) > > { > > unsigned long entries[KASAN_STACK_DEPTH]; > > unsigned int nr_entries; > > @@ -54,7 +54,7 @@ static inline depot_stack_handle_t save_stack(gfp_t flags) > > static inline void set_track(struct kasan_track *track, gfp_t flags) > > { > > track->pid = current->pid; > > - track->stack = save_stack(flags); > > + track->stack = kasan_save_stack(flags); > > } > > > > void kasan_enable_current(void) > > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c > > index 56ff8885fe2e..b86880c338e2 100644 > > --- a/mm/kasan/generic.c > > +++ b/mm/kasan/generic.c > > @@ -325,3 +325,32 @@ DEFINE_ASAN_SET_SHADOW(f2); > > DEFINE_ASAN_SET_SHADOW(f3); > > DEFINE_ASAN_SET_SHADOW(f5); > > DEFINE_ASAN_SET_SHADOW(f8); > > + > > +void kasan_record_aux_stack(void *addr) > > +{ > > + struct page *page = kasan_addr_to_page(addr); > > + struct kmem_cache *cache; > > + struct kasan_alloc_meta *alloc_info; > > + void *object; > > + > > + if (!(page && PageSlab(page))) > > + return; > > + > > + cache = page->slab_cache; > > + object = nearest_obj(cache, page, addr); > > + alloc_info = get_alloc_info(cache, object); > > + > > + if (!alloc_info->rcu_stack[0]) > > + /* record first call_rcu() call stack */ > > + alloc_info->rcu_stack[0] = kasan_save_stack(GFP_NOWAIT); > > + else > > + /* record last call_rcu() call stack */ > > + alloc_info->rcu_stack[1] = kasan_save_stack(GFP_NOWAIT); > > +} > > + > > +struct kasan_track *kasan_get_aux_stack(struct kasan_alloc_meta *alloc_info, > > + u8 idx) > > +{ > > + return container_of(&alloc_info->rcu_stack[idx], > > + struct kasan_track, stack); > > +} > > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > > index e8f37199d885..1cc1fb7b0de3 100644 > > --- a/mm/kasan/kasan.h > > +++ b/mm/kasan/kasan.h > > @@ -96,15 +96,28 @@ struct kasan_track { > > depot_stack_handle_t stack; > > }; > > > > +#ifdef CONFIG_KASAN_GENERIC > > +#define SIZEOF_PTR sizeof(void *) > > +#define KASAN_NR_RCU_CALL_STACKS 2 > > +#else /* CONFIG_KASAN_GENERIC */ > > #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY > > #define KASAN_NR_FREE_STACKS 5 > > #else > > #define KASAN_NR_FREE_STACKS 1 > > #endif > > +#endif /* CONFIG_KASAN_GENERIC */ > > > > struct kasan_alloc_meta { > > struct kasan_track alloc_track; > > +#ifdef CONFIG_KASAN_GENERIC > > + /* > > + * call_rcu() call stack is stored into struct kasan_alloc_meta. > > + * The free stack is stored into freed object. > > + */ > > + depot_stack_handle_t rcu_stack[KASAN_NR_RCU_CALL_STACKS]; > > +#else > > struct kasan_track free_track[KASAN_NR_FREE_STACKS]; > > +#endif > > #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY > > u8 free_pointer_tag[KASAN_NR_FREE_STACKS]; > > u8 free_track_idx; > > @@ -159,16 +172,22 @@ void kasan_report_invalid_free(void *object, unsigned long ip); > > > > struct page *kasan_addr_to_page(const void *addr); > > > > +depot_stack_handle_t kasan_save_stack(gfp_t flags); > > + > > #if defined(CONFIG_KASAN_GENERIC) && \ > > (defined(CONFIG_SLAB) || defined(CONFIG_SLUB)) > > void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache); > > void quarantine_reduce(void); > > void quarantine_remove_cache(struct kmem_cache *cache); > > +struct kasan_track *kasan_get_aux_stack(struct kasan_alloc_meta *alloc_info, > > + u8 idx); > > #else > > static inline void quarantine_put(struct kasan_free_meta *info, > > struct kmem_cache *cache) { } > > static inline void quarantine_reduce(void) { } > > static inline void quarantine_remove_cache(struct kmem_cache *cache) { } > > +static inline struct kasan_track *kasan_get_aux_stack( > > + struct kasan_alloc_meta *alloc_info, u8 idx) { return NULL; } > > #endif > > > > #ifdef CONFIG_KASAN_SW_TAGS > > diff --git a/mm/kasan/report.c b/mm/kasan/report.c > > index 80f23c9da6b0..f16a1a210815 100644 > > --- a/mm/kasan/report.c > > +++ b/mm/kasan/report.c > > @@ -105,9 +105,13 @@ static void end_report(unsigned long *flags) > > kasan_enable_current(); > > } > > > > -static void print_track(struct kasan_track *track, const char *prefix) > > +static void print_track(struct kasan_track *track, const char *prefix, > > + bool is_callrcu) > > { > > - pr_err("%s by task %u:\n", prefix, track->pid); > > + if (is_callrcu) > > + pr_err("%s:\n", prefix); > > + else > > + pr_err("%s by task %u:\n", prefix, track->pid); > > if (track->stack) { > > unsigned long *entries; > > unsigned int nr_entries; > > @@ -187,11 +191,20 @@ static void describe_object(struct kmem_cache *cache, void *object, > > if (cache->flags & SLAB_KASAN) { > > struct kasan_track *free_track; > > > > - print_track(&alloc_info->alloc_track, "Allocated"); > > + print_track(&alloc_info->alloc_track, "Allocated", false); > > pr_err("\n"); > > free_track = kasan_get_free_track(cache, object, tag); > > - print_track(free_track, "Freed"); > > + print_track(free_track, "Freed", false); > > pr_err("\n"); > > + > > + if (IS_ENABLED(CONFIG_KASAN_GENERIC)) { > > + free_track = kasan_get_aux_stack(alloc_info, 0); > > + print_track(free_track, "First call_rcu() call stack", true); > > + pr_err("\n"); > > + free_track = kasan_get_aux_stack(alloc_info, 1); > > + print_track(free_track, "Last call_rcu() call stack", true); > > + pr_err("\n"); > > + } > > } > > > > describe_object_addr(cache, object, addr); > > -- > I> 2.18.0
