linux-kernel - Re: [PATCH 12/15] stackdepot: add refcount for records

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Message-ID: <CA+fCnZe2ZRQe+xt9A7suXrYW8Sb7WGD+oJJVWz6Co-KGYghZLw@mail.gmail.com>
Date:   Mon, 4 Sep 2023 20:46:46 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Marco Elver <elver@...gle.com>
Cc:     andrey.konovalov@...ux.dev,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, kasan-dev@...glegroups.com,
        Evgenii Stepanov <eugenis@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH 12/15] stackdepot: add refcount for records

On Wed, Aug 30, 2023 at 11:33 AM Marco Elver <elver@...gle.com> wrote:
>
> If someone doesn't use stack_depot_evict(), and the refcount eventually
> overflows, it'll do a WARN (per refcount_warn_saturate()).
>
> I think the interface needs to be different:
>
>         stack_depot_get(): increments refcount (could be inline if just
>         wrapper around refcount_inc())
>
>         stack_depot_put(): what stack_depot_evict() currently does
>
> Then it's clear that if someone uses either stack_depot_get() or _put()
> that these need to be balanced. Not using either will result in the old
> behaviour of never evicting an entry.

So you mean the exported interface needs to be different? And the
users will need to call both stack_depot_save+stack_depot_get for
saving? Hm, this seems odd.

WDYT about adding a new flavor of stack_depot_save called
stack_depot_save_get that would increment the refcount? And renaming
stack_depot_evict to stack_depot_put.

I'm not sure though if the overflow is actually an issue. Hitting that
would require calling stack_depot_save INT_MAX times.