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From: Mike Frysinger <vapier.adi@gmail.com>
Date: Tue, 25 May 2010 13:28:19 -0400
Message-ID: <AANLkTilT3D8c86LYK2DxcNpM2F3D8iCbgY_sfUg8h58p@mail.gmail.com>
Subject: Re: [PATCH -mm 1/1] ptrace: PTRACE_GETFDPIC: fix the unsafe usage of 
	child->mm
To: Oleg Nesterov <oleg@redhat.com>
Cc: David Howells <dhowells@redhat.com>, Roland McGrath <roland@redhat.com>,
       Andrew Morton <akpm@linux-foundation.org>, linux-sh@vger.kernel.org,
       Paul Mundt <lethal@linux-sh.org>,
       uclinux-dist-devel@blackfin.uclinux.org, linux-kernel@vger.kernel.org
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On Tue, May 25, 2010 at 06:23, Oleg Nesterov wrote:
>        - arch/blackfin/kernel/ptrace.c:is_user_addr_valid()
>          needs mmap_sem around find_vma()
>
>          The lockless access to mm->context.sram_list doesn't look
>          safe to me.
>
>          If we add get_task_mm() - this protects us against
>          destroy_context() only. What is the tracee's sub-thread
>          does sys_sram_alloc() or sys_sram_free() in parallel?

i dont believe there are any code paths in UP systems where this would
be a practical problem because sram_list is only updated by syscalls
from userspace.  we probably should add proper locking to this
structure though.  i'll open a tracker item about it, thanks !
-mike