[Devel] [PATCH rh7 1/2] mm/memcg: Don't enable interrupts too soon.

[Konstantin Khorenko]

Please consider to apply these patches a as ReadyKernel patch after they pass QA in the scope of vz7 update 6.

https://readykernel.com/

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 10/30/2017 04:51 PM, Andrey Ryabinin wrote:
> When mem_cgroup_move_parent() moves huge page it disables interrupt:
>
> 	if (nr_pages > 1) {
> 		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
> 		flags = compound_lock_irqsave(page);
> 	}
>
> and calls:
> 	ret = mem_cgroup_move_account(page, nr_pages, ...
>
> which does the following:
>
> 	local_irq_disable();
> 	mem_cgroup_charge_statistics(to, page, nr_pages);
> 	...
> 	local_irq_enable();
>
> So the last local_irq_enable() enables irq too early, which may lead
> to the deadlock. mem_cgroup_move_account() should use local_irq_save()/
> local_irq_restore() primitives instead.
>
> Found while investigating https://jira.sw.ru/browse/PSBM-76011
> but unrelated.
>
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
> ---
>  mm/memcontrol.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 239fbca70b59..efc455d8ca81 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3597,15 +3597,14 @@ static int mem_cgroup_move_account(struct page *page,
>
>  	/* caller should have done css_get */
>  	pc->mem_cgroup = to;
> -	move_unlock_mem_cgroup(from, &flags);
> +	spin_unlock(&from->move_lock);
>  	ret = 0;
>
> -	local_irq_disable();
>  	mem_cgroup_charge_statistics(to, page, nr_pages);
>  	memcg_check_events(to, page);
>  	mem_cgroup_charge_statistics(from, page, -nr_pages);
>  	memcg_check_events(from, page);
> -	local_irq_enable();
> +	local_irq_restore(flags);
>  out_unlock:
>  	unlock_page(page);
>  out:
>