linux-kernel - Re: [PATCH 1/1] mm: Fix memory leak on mm

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Message-Id: <20230330124230.9f3d4f63374eb15a3b990ff8@linux-foundation.org>
Date:   Thu, 30 Mar 2023 12:42:30 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel@...r.kernel.org, Shakeel Butt <shakeelb@...gle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-mm@...ck.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/1] mm: Fix memory leak on mm_init error handling

On Thu, 30 Mar 2023 09:38:22 -0400 Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> commit f1a7941243c1 ("mm: convert mm's rss stats into percpu_counter")
> introduces a memory leak by missing a call to destroy_context() when a
> percpu_counter fails to allocate.
> 
> Before introducing the per-cpu counter allocations, init_new_context()
> was the last call that could fail in mm_init(), and thus there was no
> need to ever invoke destroy_context() in the error paths. Adding the
> following percpu counter allocations adds error paths after
> init_new_context(), which means its associated destroy_context() needs
> to be called when percpu counters fail to allocate.
> 
> ...
>
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1171,6 +1171,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
>  fail_pcpu:
>  	while (i > 0)
>  		percpu_counter_destroy(&mm->rss_stat[--i]);
> +	destroy_context(mm);
>  fail_nocontext:
>  	mm_free_pgd(mm);
>  fail_nopgd:

Is there really a leak?  I wasn't able to find a version of
init_new_context() which performs allocation.