Date: Sat, 9 Jun 2012 11:44:44 +0200
From: Johannes Weiner <hannes@cmpxchg.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, dhillf@gmail.com,
        rientjes@google.com, mhocko@suse.cz, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org
Subject: Re: [PATCH -V8 05/16] hugetlb: avoid taking i_mmap_mutex in
 unmap_single_vma() for hugetlb
Message-ID: <20120609094444.GG1761@cmpxchg.org>
References: <1339232401-14392-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
 <1339232401-14392-6-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1339232401-14392-6-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1579
Lines: 36

On Sat, Jun 09, 2012 at 02:29:50PM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.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@linux.vnet.ibm.com>

This patch (together with the previous one) seems like a bugfix that's
not really related to the hugetlb controller, unless I miss something.

Could you please submit the fix separately?

Maybe also fold the two patches into one and make it a single bugfix
change that gets rid of the lock by switching away from page->lru.

Thanks
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/