From: Yang Shi <yang.shi@linux.alibaba.com>
To: Michal Hocko <mhocko@kernel.org>, Nadav Amit <nadav.amit@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>,
ldufour@linux.vnet.ibm.com,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
acme@kernel.org, alexander.shishkin@linux.intel.com,
jolsa@redhat.com, namhyung@kernel.org,
"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping
Date: Fri, 22 Jun 2018 18:01:08 -0700 [thread overview]
Message-ID: <94bdfcf0-68ea-404c-a60f-362f677884b6@linux.alibaba.com> (raw)
In-Reply-To: <c184031d-b1db-503e-1a32-7963b4bf3de0@linux.alibaba.com>
Yes, this is true but I guess what Yang Shi meant was that an userspace
>> access racing with munmap is not well defined. You never know whether
>> you get your data, #PTF or SEGV because it depends on timing. The user
>> visible change might be that you lose content and get zero page instead
>> if you hit the race window while we are unmapping which was not possible
>> before. But whouldn't such an access pattern be buggy anyway? You need
>> some form of external synchronization AFAICS.
>>
>> But maybe some userspace depends on "getting right data or get SEGV"
>> semantic. If we have to preserve that then we can come up with a VM_DEAD
>> flag set before we tear it down and force the SEGV on the #PF path.
>> Something similar we already do for MMF_UNSTABLE.
>
> Set VM_DEAD with read mmap_sem held? It should be ok since this is the
> only place to set this flag for this unique special case.
BTW, it looks the vm flags have used up in 32 bit. If we really need
VM_DEAD, it should be for both 32-bit and 64-bit.
Any suggestion?
Thanks,
Yang
>
> Yang
>
>
next prev parent reply other threads:[~2018-06-23 1:01 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-18 23:34 [RFC v2 0/2] mm: zap pages with read mmap_sem in munmap for large mapping Yang Shi
2018-06-18 23:34 ` [RFC v2 PATCH 1/2] uprobes: make vma_has_uprobes non-static Yang Shi
2018-06-18 23:34 ` [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping Yang Shi
2018-06-19 10:02 ` Peter Zijlstra
2018-06-19 21:13 ` Yang Shi
2018-06-20 7:17 ` Michal Hocko
2018-06-20 16:23 ` Yang Shi
2018-06-19 22:17 ` Nadav Amit
[not found] ` <158a4e4c-d290-77c4-a595-71332ede392b@linux.alibaba.com>
2018-06-20 0:31 ` Nadav Amit
2018-06-20 7:18 ` Michal Hocko
2018-06-20 17:12 ` Nadav Amit
2018-06-20 18:42 ` Yang Shi
2018-06-23 1:01 ` Yang Shi [this message]
2018-06-25 9:14 ` Michal Hocko
2018-06-26 0:06 ` Yang Shi
2018-06-26 7:43 ` Peter Zijlstra
2018-06-27 1:03 ` Yang Shi
2018-06-27 7:24 ` Michal Hocko
2018-06-27 17:23 ` Yang Shi
2018-06-28 11:51 ` Michal Hocko
2018-06-28 19:10 ` Yang Shi
2018-06-29 0:59 ` Yang Shi
2018-06-29 11:39 ` Michal Hocko
2018-06-29 16:50 ` Yang Shi
2018-06-29 11:34 ` Michal Hocko
2018-06-29 16:45 ` Yang Shi
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