linux-kernel - Re: [PATCH 4/5] teach smaps_pte

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Message-ID: <1297366368.6737.14780.camel@nimitz>
Date:	Thu, 10 Feb 2011 11:32:48 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael J Wolf <mjwolf@...ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 4/5] teach smaps_pte_range() about THP pmds

On Thu, 2011-02-10 at 19:08 +0100, Andrea Arcangeli wrote:
> the locking looks wrong, who is taking the &walk->mm->page_table_lock,
> and isn't this going to deadlock on the pte_offset_map_lock for
> NR_CPUS < 4, and where is it released? This spin_lock don't seem
> necessary to me.
> 
> The right locking would be:
> 
>  spin_lock(&walk->mm->page_table_lock);
>  if (pmd_trans_huge(*pmd)) {
>    if (pmd_trans_splitting(*pmd)) {
>     spin_unlock(&walk->mm->page_table_lock);
>     wait_split_huge_page(vma->anon_vma, pmd);
>    } else {
>     smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_SIZE, walk);
>     spin_unlock(&walk->mm->page_table_lock);
>     return 0;
>   } 

I was under the assumption that the mm->page_table_lock was already held
here, but I think that's wrong.  I'll go back, take another look, and
retest.

-- Dave

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