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From: Dave Hansen <dave.hansen@intel.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Yang Shi <yang.shi@linux.alibaba.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	mhocko@kernel.org, willy@infradead.org,
	ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org,
	peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
	alexander.shishkin@linux.intel.com, jolsa@redhat.com,
	namhyung@kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC v8 PATCH 3/5] mm: mmap: zap pages with read mmap_sem in munmap
Date: Wed, 22 Aug 2018 14:42:27 -0700	[thread overview]
Message-ID: <45a5ff36-d53d-9ec3-f869-1b1b7a6de5cb@intel.com> (raw)
In-Reply-To: <20180822211053.qg3dlzf6pok2x4yk@kshutemo-mobl1>

On 08/22/2018 02:10 PM, Kirill A. Shutemov wrote:
>> For x86, mpx_notify_unmap() looks finally zap the VM_MPX vmas in bound table
>> range with zap_page_range() and doesn't update vm flags, so it sounds ok to
>> me since vmas have been detached, nobody can find those vmas. But, I'm not
>> familiar with the details of mpx, maybe Kirill could help to confirm this?
> I don't see anything obviously dependent on down_write() in
> mpx_notify_unmap(), but Dave should know better.

We need mmap_sem for write in mpx_notify_unmap().

Its job is to clean up bounds tables, but bounds tables are dynamically
allocated and destroyed by the kernel.  When we destroy a table, we also
destroy the VMA for the bounds table *itself*, separate from the VMA
being unmapped.

But, this code is very likely to go away soon.  If it's causing a
problem for you, let me know and I'll see if I can get to removing it
faster.

  reply	other threads:[~2018-08-22 21:42 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-15 18:49 [RFC v8 PATCH 0/5] mm: zap pages with read mmap_sem in munmap for large mapping Yang Shi
2018-08-15 18:49 ` [RFC v8 PATCH 1/5] mm: refactor do_munmap() to extract the common part Yang Shi
2018-08-15 18:49 ` [RFC v8 PATCH 2/5] uprobes: introduce has_uprobes helper Yang Shi
2018-08-22 10:55   ` Vlastimil Babka
2018-08-22 15:07     ` Srikar Dronamraju
2018-08-22 20:51       ` Yang Shi
2018-08-23 15:15       ` Oleg Nesterov
2018-08-23 16:07         ` Yang Shi
2018-08-15 18:49 ` [RFC v8 PATCH 3/5] mm: mmap: zap pages with read mmap_sem in munmap Yang Shi
2018-08-15 19:16   ` Matthew Wilcox
2018-08-15 21:09     ` Matthew Wilcox
2018-08-15 21:54       ` Yang Shi
2018-08-16  2:46         ` Matthew Wilcox
2018-08-16  6:11           ` Yang Shi
2018-08-22 11:11   ` Vlastimil Babka
2018-08-22 19:20     ` Yang Shi
2018-08-22 11:19   ` Vlastimil Babka
2018-08-22 20:45     ` Yang Shi
2018-08-22 21:10       ` Kirill A. Shutemov
2018-08-22 21:42         ` Dave Hansen [this message]
2018-08-22 21:56           ` Yang Shi
2018-08-22 22:03             ` Dave Hansen
2018-08-15 18:49 ` [RFC v8 PATCH 4/5] mm: unmap VM_HUGETLB mappings with optimized path Yang Shi
2018-08-15 18:49 ` [RFC v8 PATCH 5/5] mm: unmap VM_PFNMAP " Yang Shi

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