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From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 2 Feb 2023 11:03:52 +0100
Message-ID: <CAG_fn=Uw6CA+N-dd6e_gp+AhogohBUU0XyNCTtjF6MZC_fgiCA@mail.gmail.com>
Subject: Re: [PATCH 15/18] lib/stacktrace, kasan, kmsan: rework extra_bits interface
To:     andrey.konovalov@linux.dev
Cc:     Marco Elver <elver@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        Evgenii Stepanov <eugenis@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
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> This change also fixes a minor issue in the old code: __stack_depot_save
> does not return NULL if saving stack trace fails and extra_bits is used.

Good catch!


> + *
> + * Stack depot handles have a few unused bits, which can be used for storing
> + * user-specific information. These bits are transparent to the stack depot.
> + */
> +depot_stack_handle_t stack_depot_set_extra_bits(depot_stack_handle_t handle,
> +                                               unsigned int extra_bits)
> +{
> +       union handle_parts parts = { .handle = handle };
> +
> +       parts.extra = extra_bits;
> +       return parts.handle;
> +}
> +EXPORT_SYMBOL(stack_depot_set_extra_bits);

You'd need to check for handle==NULL here, otherwise we're in the same
situation when __stack_depot_save returns NULL and we are happily
applying extra bits on top of it.