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

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





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