linux-kernel - Re: [PATCH 09/10] huge pagecache: mmap_sem is unlocked when truncation splits pmd

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 for Android: free password hash cracker in your pocket

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

Date:	Mon, 11 Apr 2016 13:35:08 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Yang Shi <yang.shi@...aro.org>, Ning Qu <quning@...il.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 09/10] huge pagecache: mmap_sem is unlocked when
 truncation splits pmd

On Tue, Apr 05, 2016 at 01:55:23PM -0700, Hugh Dickins wrote:
> zap_pmd_range()'s CONFIG_DEBUG_VM !rwsem_is_locked(&mmap_sem) BUG()
> will be invalid with huge pagecache, in whatever way it is implemented:
> truncation of a hugely-mapped file to an unhugely-aligned size would
> easily hit it.
> 
> (Although anon THP could in principle apply khugepaged to private file
> mappings, which are not excluded by the MADV_HUGEPAGE restrictions, in
> practice there's a vm_ops check which excludes them, so it never hits
> this BUG() - there's no interface to "truncate" an anonymous mapping.)
> 
> We could complicate the test, to check i_mmap_rwsem also when there's a
> vm_file; but my inclination was to make zap_pmd_range() more readable by
> simply deleting this check.  A search has shown no report of the issue in
> the years since commit e0897d75f0b2 ("mm, thp: print useful information
> when mmap_sem is unlocked in zap_pmd_range") expanded it from VM_BUG_ON()
> - though I cannot point to what commit I would say then fixed the issue.
> 
> But there are a couple of other patches now floating around, neither
> yet in the tree: let's agree to retain the check as a VM_BUG_ON_VMA(),
> as Matthew Wilcox has done; but subject to a vma_is_anonymous() check,
> as Kirill Shutemov has done.  And let's get this in, without waiting
> for any particular huge pagecache implementation to reach the tree.
> 
> Signed-off-by: Hugh Dickins <hughd@...gle.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov