Re: [PATCH v4 1/4] rcu/kasan: record and print call_rcu() call stack

Walter Wu
2020-05-20T02:45:27Z

Hi Andrey,

On Tue, 2020-05-19 at 16:52 +0200, 'Andrey Konovalov' via kasan-dev
wrote:
> On Tue, May 19, 2020 at 4:24 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
> >
> > This feature will record the last two call_rcu() call stacks and
> > prints up to 2 call_rcu() call stacks in KASAN report.
> >
> > When call_rcu() is called, we store the call_rcu() call stack into
> > slub alloc meta-data, so that the KASAN report can print rcu stack.
> >
> > [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@mediatek.com>
> > Suggested-by: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Alexander Potapenko <glider@google.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Paul E. McKenney <paulmck@kernel.org>
> > Cc: Josh Triplett <josh@joshtriplett.org>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> > Cc: Joel Fernandes <joel@joelfernandes.org>
> > ---
> > include/linux/kasan.h | 2 ++
> > kernel/rcu/tree.c | 2 ++
> > lib/Kconfig.kasan | 2 ++
> > mm/kasan/common.c | 4 ++--
> > mm/kasan/generic.c | 19 +++++++++++++++++++
> > mm/kasan/kasan.h | 10 ++++++++++
> > mm/kasan/report.c | 24 ++++++++++++++++++++++++
> > 7 files changed, 61 insertions(+), 2 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..36a4ff7f320b 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"
> > @@ -2668,6 +2669,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
> > head->func = func;
> > head->next = NULL;
> > local_irq_save(flags);
> > + kasan_record_aux_stack(head);
> > rdp = this_cpu_ptr(&rcu_data);
> >
> > /* Add the callback to our list. */
> > diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> > index 81f5464ea9e1..4e83cf6e3caa 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).
> > + In generic mode KASAN prints the last two call_rcu() call stacks in
> > + reports.
>
> I don't think we need this here, mentioning this in the documentation is fine.
>

Ok, we will remove it. Only mention it in the documentation.

>
> >
> > 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..3372bdcaf92a 100644
> > --- a/mm/kasan/generic.c
> > +++ b/mm/kasan/generic.c
> > @@ -325,3 +325,22 @@ 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);
> > +
> > + /* record the last two call_rcu() call stacks */
> > + alloc_info->aux_stack[1] = alloc_info->aux_stack[0];
> > + alloc_info->aux_stack[0] = kasan_save_stack(GFP_NOWAIT);
> > +}
> > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> > index e8f37199d885..a7391bc83070 100644
> > --- a/mm/kasan/kasan.h
> > +++ b/mm/kasan/kasan.h
> > @@ -104,7 +104,15 @@ struct kasan_track {
> >
> > 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 struct kasan_free_meta.
> > + */
> > + depot_stack_handle_t aux_stack[2];
> > +#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;
> > @@ -159,6 +167,8 @@ 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);
> > diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> > index 80f23c9da6b0..6f8f2bf8f53b 100644
> > --- a/mm/kasan/report.c
> > +++ b/mm/kasan/report.c
> > @@ -179,6 +179,17 @@ static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> > return &alloc_meta->free_track[i];
> > }
> >
> > +#ifdef CONFIG_KASAN_GENERIC
> > +static void print_stack(depot_stack_handle_t stack)
>
> Let's put this function just before print_track() and reuse there.
>

Ok.

> > +{
> > + unsigned long *entries;
> > + unsigned int nr_entries;
> > +
> > + nr_entries = stack_depot_fetch(stack, &entries);
> > + stack_trace_print(entries, nr_entries, 0);
> > +}
> > +#endif
> > +
> > static void describe_object(struct kmem_cache *cache, void *object,
> > const void *addr, u8 tag)
> > {
> > @@ -192,6 +203,19 @@ static void describe_object(struct kmem_cache *cache, void *object,
> > free_track = kasan_get_free_track(cache, object, tag);
> > print_track(free_track, "Freed");
> > pr_err("\n");
> > +
> > +#ifdef CONFIG_KASAN_GENERIC
> > + if (alloc_info->aux_stack[0]) {
> > + pr_err("Last one call_rcu() call stack:\n");
>
> Could you change this to "Last call_rcu():\n",
>
> > + print_stack(alloc_info->aux_stack[0]);
> > + pr_err("\n");
> > + }
> > + if (alloc_info->aux_stack[1]) {
> > + pr_err("Second to last call_rcu() call stack:\n");
>
> and this to "Second to last call_rcu():\n"?
>
> It's shorter, but provides the same info.
>

We will change their name.

Thank you for your review.

>
>
> > + print_stack(alloc_info->aux_stack[1]);
> > + pr_err("\n");
> > + }
> > +#endif
> > }
> >
> > describe_object_addr(cache, object, addr);
> > --
> > 2.18.0
> >
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>