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

[Walter Wu]

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@xxxxxxxxxxxx> 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@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     |  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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>