On Tue, Nov 30, 2021 at 11:14 AM Marco Elver <elver@xxxxxxxxxx> wrote: > > The non-interrupt portion of interrupt stack traces before interrupt > entry is usually arbitrary. Therefore, saving stack traces of interrupts > (that include entries before interrupt entry) to stack depot leads to > unbounded stackdepot growth. > > As such, use of filter_irq_stacks() is a requirement to ensure > stackdepot can efficiently deduplicate interrupt stacks. > > Looking through all current users of stack_depot_save(), none (except > KASAN) pass the stack trace through filter_irq_stacks() before passing > it on to stack_depot_save(). > > Rather than adding filter_irq_stacks() to all current users of > stack_depot_save(), it became clear that stack_depot_save() should > simply do filter_irq_stacks(). > > Signed-off-by: Marco Elver <elver@xxxxxxxxxx> > --- > lib/stackdepot.c | 13 +++++++++++++ > mm/kasan/common.c | 1 - > 2 files changed, 13 insertions(+), 1 deletion(-) > > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > index b437ae79aca1..519c7898c7f2 100644 > --- a/lib/stackdepot.c > +++ b/lib/stackdepot.c > @@ -305,6 +305,9 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch); > * (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids > * any allocations and will fail if no space is left to store the stack trace. > * > + * If the stack trace in @entries is from an interrupt, only the portion up to > + * interrupt entry is saved. > + * > * Context: Any context, but setting @can_alloc to %false is required if > * alloc_pages() cannot be used from the current context. Currently > * this is the case from contexts where neither %GFP_ATOMIC nor > @@ -323,6 +326,16 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, > unsigned long flags; > u32 hash; > > + /* > + * If this stack trace is from an interrupt, including anything before > + * interrupt entry usually leads to unbounded stackdepot growth. > + * > + * Because use of filter_irq_stacks() is a requirement to ensure > + * stackdepot can efficiently deduplicate interrupt stacks, always > + * filter_irq_stacks() to simplify all callers' use of stackdepot. > + */ > + nr_entries = filter_irq_stacks(entries, nr_entries); > + > if (unlikely(nr_entries == 0) || stack_depot_disable) > goto fast_exit; > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 8428da2aaf17..efaa836e5132 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -36,7 +36,6 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc) > unsigned int nr_entries; > > nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0); > - nr_entries = filter_irq_stacks(entries, nr_entries); > return __stack_depot_save(entries, nr_entries, flags, can_alloc); > } > > -- > 2.34.0.rc2.393.gf8c9666880-goog > Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
