linux-kernel - Re: [patch v2] mm, thp: print useful information when mmap_sem is unlocked in zap_pmd

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Date:	Fri, 22 Jun 2012 14:06:40 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Jones <davej@...hat.com>
cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrea Arcangeli <aarcange@...hat.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch v2] mm, thp: print useful information when mmap_sem is
 unlocked in zap_pmd_range

On Mon, 11 Jun 2012, David Rientjes wrote:

> diff --git a/mm/memory.c b/mm/memory.c
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1225,7 +1225,15 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
>  		next = pmd_addr_end(addr, end);
>  		if (pmd_trans_huge(*pmd)) {
>  			if (next - addr != HPAGE_PMD_SIZE) {
> -				VM_BUG_ON(!rwsem_is_locked(&tlb->mm->mmap_sem));
> +#ifdef CONFIG_DEBUG_VM
> +				if (!rwsem_is_locked(&tlb->mm->mmap_sem)) {
> +					pr_err("%s: mmap_sem is unlocked! addr=0x%lx end=0x%lx vma->vm_start=0x%lx vma->vm_end=0x%lx\n",
> +						__func__, addr, end,
> +						vma->vm_start,
> +						vma->vm_end);
> +					BUG();
> +				}
> +#endif
>  				split_huge_page_pmd(vma->vm_mm, pmd);
>  			} else if (zap_huge_pmd(tlb, vma, pmd, addr))
>  				goto next;

This patch is now in Linus' tree so if you are able to hit this issue and 
capture it again, we should be able to get much more useful information.
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