From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Andres Lagar-Cavilla <andreslc@google.com>,
Yang Shi <yang.shi@linaro.org>, Ning Qu <quning@gmail.com>,
Matthew Wilcox <willy@linux.intel.com>,
David Rientjes <rientjes@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 09/10] huge pagecache: mmap_sem is unlocked when truncation splits pmd
Date: Mon, 11 Apr 2016 13:35:08 +0300 [thread overview]
Message-ID: <20160411103508.GC22996@node.shutemov.name> (raw)
In-Reply-To: <alpine.LSU.2.11.1604051352540.5965@eggly.anvils>
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@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
--
Kirill A. Shutemov
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next prev parent reply other threads:[~2016-04-11 10:35 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-05 20:37 [PATCH 00/10] mm: easy preliminaries to THPagecache Hugh Dickins
2016-04-05 20:40 ` [PATCH 01/10] mm: update_lru_size warn and reset bad lru_size Hugh Dickins
2016-04-14 11:56 ` Vlastimil Babka
2016-04-05 20:42 ` [PATCH 02/10] mm: update_lru_size do the __mod_zone_page_state Hugh Dickins
2016-04-05 20:44 ` [PATCH 03/10] mm: use __SetPageSwapBacked and dont ClearPageSwapBacked Hugh Dickins
2016-04-06 9:52 ` Mel Gorman
2016-04-05 20:45 ` [PATCH 04/10] tmpfs: preliminary minor tidyups Hugh Dickins
2016-04-05 20:47 ` [PATCH 05/10] tmpfs: mem_cgroup charge fault to vm_mm not current mm Hugh Dickins
2016-04-05 20:49 ` [PATCH 06/10] mm: /proc/sys/vm/stat_refresh to force vmstat update Hugh Dickins
2016-04-05 20:51 ` [PATCH 07/10] huge mm: move_huge_pmd does not need new_vma Hugh Dickins
2016-04-11 10:28 ` Kirill A. Shutemov
2016-04-05 20:52 ` [PATCH 08/10] huge pagecache: extend mremap pmd rmap lockout to files Hugh Dickins
2016-04-11 10:32 ` Kirill A. Shutemov
2016-04-05 20:55 ` [PATCH 09/10] huge pagecache: mmap_sem is unlocked when truncation splits pmd Hugh Dickins
2016-04-11 10:35 ` Kirill A. Shutemov [this message]
2016-04-14 17:39 ` Matthew Wilcox
2016-04-16 4:55 ` Andrew Morton
2016-04-05 21:02 ` [PATCH 10/10] arch: fix has_transparent_hugepage() Hugh Dickins
2016-04-05 23:25 ` David Miller
2016-04-06 3:22 ` Vineet Gupta
2016-04-06 6:58 ` Ingo Molnar
2016-04-06 12:29 ` Chris Metcalf
2016-04-06 21:58 ` Ingo Molnar
2016-04-06 11:56 ` Gerald Schaefer
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