linux-kernel - Re: [PATCH -V9 05/15] hugetlb: avoid taking i_mmap_mutex in unmap_single

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Message-ID: <4FD955E8.5050100@jp.fujitsu.com>
Date:	Thu, 14 Jun 2012 12:09:28 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
CC:	linux-mm@...ck.org, dhillf@...il.com, rientjes@...gle.com,
	mhocko@...e.cz, akpm@...ux-foundation.org, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH -V9 05/15] hugetlb: avoid taking i_mmap_mutex in unmap_single_vma()
 for hugetlb

(2012/06/13 19:27), Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V"<aneesh.kumar@...ux.vnet.ibm.com>
> 
> i_mmap_mutex lock was added in unmap_single_vma by 502717f4e ("hugetlb:
> fix linked list corruption in unmap_hugepage_range()") but we don't use
> page->lru in unmap_hugepage_range any more.  Also the lock was taken
> higher up in the stack in some code path.  That would result in deadlock.
> 
> unmap_mapping_range (i_mmap_mutex)
>   ->  unmap_mapping_range_tree
>      ->  unmap_mapping_range_vma
>         ->  zap_page_range_single
>           ->  unmap_single_vma
> 	      ->  unmap_hugepage_range (i_mmap_mutex)
> 
> For shared pagetable support for huge pages, since pagetable pages are ref
> counted we don't need any lock during huge_pmd_unshare.  We do take
> i_mmap_mutex in huge_pmd_share while walking the vma_prio_tree in mapping.
> (39dde65c9940c97f ("shared page table for hugetlb page")).
> 
> Signed-off-by: Aneesh Kumar K.V<aneesh.kumar@...ux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujtisu.com>


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