From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@elte.hu>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
Anton Arapov <anton@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] uprobes: write_opcode()->__replace_page() can race with try_to_unmap()
Date: Fri, 08 Jun 2012 10:47:07 +0200 [thread overview]
Message-ID: <1339145227.23343.42.camel@twins> (raw)
In-Reply-To: <20120607170041.GC31974@redhat.com>
On Thu, 2012-06-07 at 19:00 +0200, Oleg Nesterov wrote:
> write_opcode() gets old_page via get_user_pages() and then calls
> __replace_page() which assumes that this old_page is still mapped
> after pte_offset_map_lock().
>
> This is not true if this old_page was already try_to_unmap()'ed,
> and in this case everything __replace_page() does with old_page
> is wrong. Just for example, put_page() is not balanced.
>
> I think it is possible to teach __replace_page() to handle this
> unlikely case correctly, but this patch simply changes it to use
> page_check_address() and return -EAGAIN if it fails. The caller
> should notice this error code and retry.
Note that replace_page() was nicked from ksm, does that suffer a similar
problem?
next prev parent reply other threads:[~2012-06-08 8:47 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-07 16:59 [PATCH 0/3] uprobes fixes for 3.5 Oleg Nesterov
2012-06-07 17:00 ` [PATCH 1/3] uprobes: valid_vma() should reject VM_HUGETLB Oleg Nesterov
2012-06-15 6:22 ` Srikar Dronamraju
2012-06-07 17:00 ` [PATCH 2/3] uprobes: __copy_insn() should ensure a_ops->readpage != NULL Oleg Nesterov
2012-06-15 6:25 ` Srikar Dronamraju
2012-06-15 12:10 ` Ingo Molnar
2012-06-07 17:00 ` [PATCH 3/3] uprobes: write_opcode()->__replace_page() can race with try_to_unmap() Oleg Nesterov
2012-06-08 8:47 ` Peter Zijlstra [this message]
2012-06-08 10:03 ` Oleg Nesterov
2012-06-08 16:55 ` Oleg Nesterov
2012-06-15 6:12 ` Srikar Dronamraju
2012-06-15 12:11 ` Ingo Molnar
2012-06-15 15:48 ` Oleg Nesterov
2012-06-16 7:11 ` Ingo Molnar
2012-06-08 14:03 ` oom-killer is crazy? (Was: [PATCH 0/3] uprobes fixes for 3.5) Oleg Nesterov
2012-06-08 14:26 ` Dave Jones
2012-06-08 15:04 ` Oleg Nesterov
2012-06-08 20:21 ` [patch for-3.5-rc1] mm, oom: fix badness score underflow David Rientjes
2012-06-09 22:25 ` KOSAKI Motohiro
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