From: Oleg Nesterov <oleg@redhat.com>
To: David Miller <davem@davemloft.net>
Cc: peterz@infradead.org, cl@linux.com, tkhai@yandex.ru,
ktkhai@parallels.com, linux-kernel@vger.kernel.org,
mingo@redhat.com, vdavydov@parallels.com
Subject: Re: introduce probe_slab_address?
Date: Wed, 22 Oct 2014 22:20:27 +0200 [thread overview]
Message-ID: <20141022202027.GA13781@redhat.com> (raw)
In-Reply-To: <20141022.160845.1338578429923954456.davem@davemloft.net>
On 10/22, David Miller wrote:
>
> From: Oleg Nesterov <oleg@redhat.com>
> Date: Wed, 22 Oct 2014 21:42:28 +0200
>
> > Now the question: is this LOAD is safe in case when this (freed) page
> > already has another mapping? This is black magic to me, I do not know.
> > And Peter has some concerns.
>
> It is immatieral, because you can read garbage and it's "don't care"
> in this context.
>
> And later if it is used again at this virtual address, it will be
> initialized with stores at that virtual address first.
>
> So no problem.
Great, thanks.
> > And, say, copy_from_user_page() on sparc does
> >
> > flush_cache_page();
> > memcpy();
> > flush_ptrace_access();
>
> In this case, as I tried to explain, it matters because the physical
> address is being accessed from two virtual address at the same time
> "for the same usage".
>
> That's what distinguishes this from the SLAB and RCU cases you cite.
Yes, this was my (vague) understanding, but thanks for another
explanation anyway.
Oleg.
next prev parent reply other threads:[~2014-10-22 20:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-20 10:15 [PATCH v3] sched/numa: fix unsafe get_task_struct() in task_numa_assign() Kirill Tkhai
2014-10-20 14:47 ` Oleg Nesterov
2014-10-20 16:56 ` Oleg Nesterov
2014-10-20 18:27 ` Oleg Nesterov
2014-10-20 20:18 ` Kirill Tkhai
2014-10-20 20:50 ` Oleg Nesterov
2014-10-20 21:05 ` Kirill Tkhai
2014-10-20 21:34 ` Oleg Nesterov
2014-10-20 22:57 ` Peter Zijlstra
2014-10-21 9:45 ` Peter Zijlstra
2014-10-21 19:03 ` Oleg Nesterov
2014-10-21 20:03 ` Kirill Tkhai
2014-10-21 20:10 ` Kirill Tkhai
2014-10-22 9:09 ` Peter Zijlstra
2014-10-22 16:14 ` Oleg Nesterov
2014-10-22 16:37 ` Peter Zijlstra
2014-10-22 18:14 ` introduce probe_slab_address? (Was: sched/numa: fix unsafe get_task_struct() in task_numa_assign()) Oleg Nesterov
2014-10-22 18:59 ` introduce probe_slab_address? David Miller
2014-10-22 19:42 ` Oleg Nesterov
2014-10-22 20:08 ` David Miller
2014-10-22 20:20 ` Oleg Nesterov [this message]
2014-10-24 9:44 ` Peter Zijlstra
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