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Re: [Xen-devel] [PATCH] xen: don't longjmp() after domain_crash() in check_wakeup_from_wait()


  • To: Juergen Gross <jgross@xxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 29 Jul 2019 10:27:50 +0100
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  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, WeiLiu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
  • Delivery-date: Mon, 29 Jul 2019 09:28:01 +0000
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On 29/07/2019 09:49, Juergen Gross wrote:
> On 29.07.19 10:34, Andrew Cooper wrote:
>> On 29/07/2019 05:36, Juergen Gross wrote:
>>> Continuing on the stack saved by __prepare_to_wait() on the wrong cpu
>>> is rather dangerous.
>>>
>>> Instead of doing so just call the scheduler again as it already is
>>> happening in the similar case in __prepare_to_wait() when doing the
>>> setjmp() would be wrong.
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>
>> I'm afraid this is still problematic.  By successfully invoking the
>> waitqueue, we know that no spinlocks were held, but we have no guarantee
>> that e.g. an xmalloc()'d pointer is still only stashed in the stack.
>
> But how are the domain_crash() invocations with following do_softirq()
> calls in the __prepare_to_wait() case fine then?

You make a very good point.

Seeing as this patch returns it to "no worse than before", and this code
isn't long for the world anyway, Reviewed-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>

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