[PATCH 1/1] mm: Fix memory leak on mm_init error handling

[PATCH 1/1] mm: Fix memory leak on mm_init error handling

[Mathieu Desnoyers]

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.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: linux-mm@kvack.org
Cc: stable@vger.kernel.org # 6.2
---
 kernel/fork.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index c0257cbee093..c983c4fe3090 100644
--- 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:
-- 
2.25.1

Re: [PATCH 1/1] mm: Fix memory leak on mm_init error handling

[Shakeel Butt]

On Thu, Mar 30, 2023 at 09:38:22AM -0400, Mathieu Desnoyers 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.
> 

Fixes: f1a7941243c1 ("mm: convert mm's rss stats into percpu_counter")

> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: linux-mm@kvack.org
> Cc: stable@vger.kernel.org # 6.2

Acked-by: Shakeel Butt <shakeelb@google.com>

Re: [PATCH 1/1] mm: Fix memory leak on mm_init error handling

[Andrew Morton]

On Thu, 30 Mar 2023 09:38:22 -0400 Mathieu Desnoyers <mathieu.desnoyers@efficios.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.

Re: [PATCH 1/1] mm: Fix memory leak on mm_init error handling

[Shakeel Butt]

On Thu, Mar 30, 2023 at 12:42 PM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> On Thu, 30 Mar 2023 09:38:22 -0400 Mathieu Desnoyers <mathieu.desnoyers@efficios.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.
>

There are more than 20 archs defining this function and I couldn't
check each one of them. I think we can assume there might be new
allocation in the future.

Re: [PATCH 1/1] mm: Fix memory leak on mm_init error handling

[Mathieu Desnoyers]

On 2023-03-30 15:42, Andrew Morton wrote:
> On Thu, 30 Mar 2023 09:38:22 -0400 Mathieu Desnoyers <mathieu.desnoyers@efficios.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.

AFAIU, at least on powerpc:

arch/powerpc/mm/book3s64/mmu_context.c: init_new_context() calls 
radix__init_new_context() or hash__init_new_context() which
leak IDs through ida_alloc_range.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com