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SubjectRe: [PATCH] lib/stackdepot: always do filter_irq_stacks() in stack_depot_save()
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On 11/30/21 10:57, Marco Elver 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().

Agree.

> Signed-off-by: Marco Elver <elver@google.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks.

> ---
> 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);
> }
>
>

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