From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K.V" Subject: Re: [PATCH -V7 05/14] hugetlb: avoid taking i_mmap_mutex in unmap_single_vma() for hugetlb Date: Thu, 31 May 2012 10:55:40 +0530 Message-ID: <20120531052540.GA24855@skywalker.linux.vnet.ibm.com> References: <1338388739-22919-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1338388739-22919-6-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Rientjes Cc: linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, dhillf@gmail.com, mhocko@suse.cz, akpm@linux-foundation.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Andrea Arcangeli On Wed, May 30, 2012 at 06:57:47PM -0700, David Rientjes wrote: > On Wed, 30 May 2012, Aneesh Kumar K.V wrote: > > > From: "Aneesh Kumar K.V" > > > > 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) > > > > You should be able to show this with lockdep? I was not able to get a lockdep report > > > 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")). > > > > I think this should be folded into patch 4, the code you're removing here > is just added in that function unnecessarily. > I am removing i_mmap_mutex in this patch. That is not added in patch 4. -aneesh