From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Yang Shi <yang.shi@linux.alibaba.com>,
Dave Hansen <dave.hansen@intel.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: Thu, 23 Aug 2018 00:10:53 +0300 [thread overview]
Message-ID: <20180822211053.qg3dlzf6pok2x4yk@kshutemo-mobl1> (raw)
In-Reply-To: <3c62f605-2244-6a05-2dc4-34a3f1c56300@linux.alibaba.com>
On Wed, Aug 22, 2018 at 01:45:44PM -0700, Yang Shi wrote:
>
>
> On 8/22/18 4:19 AM, Vlastimil Babka wrote:
> > On 08/15/2018 08:49 PM, Yang Shi wrote:
> > > + downgrade_write(&mm->mmap_sem);
> > > +
> > > + /* Zap mappings with read mmap_sem */
> > > + unmap_region(mm, start_vma, prev, start, end);
> > > +
> > > + arch_unmap(mm, start_vma, start, end);
> > Hmm, did you check that all architectures' arch_unmap() is safe with
> > read mmap_sem instead of write mmap_sem? E.g. x86 does
> > mpx_notify_unmap() there where I would be far from sure at first glance...
>
> Yes, I'm also not quite sure if it is 100% safe or not. I was trying to move
> this before downgrade_write, however, I'm not sure if it is ok or not too,
> so I keep the calling sequence.
>
> For architectures, just x86 and ppc really do something. PPC just uses it
> for vdso unmap which should just happen during process exit, so it sounds
> safe.
>
> 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.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2018-08-22 21:11 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 [this message]
2018-08-22 21:42 ` Dave Hansen
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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