linux-kernel - Re: [PATCH -V8 05/16] hugetlb: avoid taking i_mmap_mutex in unmap_single

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20120609144918.GI1761@cmpxchg.org>
Date:	Sat, 9 Jun 2012 16:49:18 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	linux-mm@...ck.org, kamezawa.hiroyu@...fujitsu.com,
	dhillf@...il.com, rientjes@...gle.com, mhocko@...e.cz,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org
Subject: Re: [PATCH -V8 05/16] hugetlb: avoid taking i_mmap_mutex in
 unmap_single_vma() for hugetlb

On Sat, Jun 09, 2012 at 06:33:05PM +0530, Aneesh Kumar K.V wrote:
> Johannes Weiner <hannes@...xchg.org> writes:
> 
> > On Sat, Jun 09, 2012 at 02:29:50PM +0530, 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>
> >
> > 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?
> 
> Patches upto 6 can really got in a separate series. I was not sure
> whether I should split them. I will post that as a separate series now

Ok, thanks, that will make it easier to upstream the controller.

> > 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.
> 
> I wanted to make sure the patch that drop i_mmap_mutex is a separate one
> so that we understand and document the locking details separately

Nothing prevents you from writing a proper changelog :-) But changing
from page->lru to an on-stack array does not have any merit by itself,
so it just seems like a needless dependency between two patches that
fix one problem (pita for backports into stable/distro kernels).
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/