linux-kernel - Re: [PATCH] hugetlb_cgroup: use lockdep_assert_held rather than spin_is

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Message-ID: <87r40l67dg.fsf@linux.vnet.ibm.com>
Date:	Tue, 12 Aug 2014 21:13:39 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hugetlb_cgroup: use lockdep_assert_held rather than spin_is_locked

Michal Hocko <mhocko@...e.cz> writes:

> spin_lock may be an empty struct for !SMP configurations and so
> arch_spin_is_locked may return unconditional 0 and trigger the VM_BUG_ON
> even when the lock is held.
>
> Replace spin_is_locked by lockdep_assert_held. We will not BUG anymore
> but it is questionable whether crashing makes a lot of sense in the
> uncharge path. Uncharge happens after the last page reference was
> released so nobody should touch the page and the function doesn't update
> any shared state except for res counter which uses synchronization of
> its own.

We do update the hugepage's hugetlb cgroup details. But as you mentioned,
this should not be an issue because we are in hugepage free.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> ---
>  mm/hugetlb_cgroup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
> index 9aae6f47433f..9edf189a5ef3 100644
> --- a/mm/hugetlb_cgroup.c
> +++ b/mm/hugetlb_cgroup.c
> @@ -217,7 +217,7 @@ void hugetlb_cgroup_uncharge_page(int idx, unsigned long nr_pages,
>
>  	if (hugetlb_cgroup_disabled())
>  		return;
> -	VM_BUG_ON(!spin_is_locked(&hugetlb_lock));
> +	lockdep_assert_held(&hugetlb_lock);
>  	h_cg = hugetlb_cgroup_from_page(page);
>  	if (unlikely(!h_cg))
>  		return;
> -- 
> 2.1.0.rc1

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