Re: [PATCH v2 1/3] rcu/kasan: record and print call_rcu() call stack

From: Walter Wu
Date: Mon May 11 2020 - 08:54:22 EST

On Mon, 2020-05-11 at 14:20 +0200, 'Dmitry Vyukov' via kasan-dev wrote:
> On Mon, May 11, 2020 at 4:31 AM Walter Wu <walter-zh.wu@xxxxxxxxxxxx> wrote:
> >
> > This feature will record first and last call_rcu() call stack and
> > print two call_rcu() call stack in KASAN report.
> >
> > 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);
> > +
> > /* 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);
>
> This is not type safe, there is no kasan_track object. And we create a
> pointer to kasan_track just to carefully not treat it as valid
> kasan_track in print_track.
>

Good catch.

> This adds an unnecessary if to print_track. And does not seem to be
> useful/nice to print:
>
> First call_rcu() call stack:
> (stack is not available)
>
> Last call_rcu() call stack:
> (stack is not available)
>
> when no rcu stacks are memorized.
> Your intention seems to be to reuse 2 lines of code from print_track.
> I would factor them out into a function:
>
> static void print_stack(depot_stack_handle_t stack)
> {
> unsigned long *entries;
> unsigned int nr_entries;
>
> nr_entries = stack_depot_fetch(stack, &entries);
> stack_trace_print(entries, nr_entries, 0);
> }
>
> And then this can expressed as:
>
> if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> stack = alloc_info->rcu_stack[0];
> if (stack) {
> pr_err("First call_rcu() call stack:\n");
> print_stack(stack);
> pr_err("\n");
> }
> stack = alloc_info->rcu_stack[1];
> if (stack) {
> pr_err("Last call_rcu() call stack:\n");
> print_stack(stack);
> pr_err("\n");
> }
> }
>

rcu_stack doesn't exist at report.c, it need at generic.c,
otherwise it will have build error, unless add the #ifdef GENERIC_KASAN

Maybe we can make kasan_get_aux_stack() return NULL? then print_stack()
determine whether it will print aux stack.

>
> Or with another helper function it becomes:
>
> if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> print_aux_stack(alloc_info->rcu_stack[0], "First");
> print_aux_stack(alloc_info->rcu_stack[1], "Last");
> }
>
>
> > +}
> > 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);
> > --
> > 2.18.0
> >
> > --
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>