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Date: Tue, 15 Sep 2015 22:01:44 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Sasha Levin <sasha.levin@oracle.com>
Cc: Hugh Dickins <hughd@google.com>, Andrey Konovalov <andreyknvl@google.com>,
        Oleg Nesterov <oleg@redhat.com>, Rik van Riel <riel@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dmitry Vyukov <dvyukov@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Vlastimil Babka <vbabka@suse.cz>
Subject: Re: Multiple potential races on vma->vm_flags
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On Tue, Sep 15, 2015 at 01:36:45PM -0400, Sasha Levin wrote:
> On 09/11/2015 09:27 PM, Hugh Dickins wrote:
> > I'm inclined to echo Vlastimil's comment from earlier in the thread:
> > sounds like an overkill, unless we find something more serious than this.
> 
> I've modified my tests to stress the exit path of processes with many vmas,

Could you share the test?

> and hit the following NULL ptr deref (not sure if it's related to the original issue):
> 
> [1181047.935563] kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC KASAN
> [1181047.937223] Modules linked in:
> [1181047.937772] CPU: 4 PID: 21912 Comm: trinity-c341 Not tainted 4.3.0-rc1-next-20150914-sasha-00043-geddd763-dirty #2554
> [1181047.939387] task: ffff8804195c8000 ti: ffff880433f00000 task.ti: ffff880433f00000
> [1181047.940533] RIP: unmap_vmas (mm/memory.c:1337)

Is it "struct mm_struct *mm = vma->vm_mm;"?

-- 
 Kirill A. Shutemov