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Re: [Xen-devel] [PATCH] timers: limit heap size
- To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 9 Apr 2019 14:38:42 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, 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>
- Delivery-date: Tue, 09 Apr 2019 13:45:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 09/04/2019 14:01, Jan Beulich wrote:
> @@ -463,9 +463,14 @@ static void timer_softirq_action(void)
> if ( unlikely(ts->list != NULL) )
> {
> /* old_limit == (2^n)-1; new_limit == (2^(n+4))-1 */
> - int old_limit = heap_metadata(heap)->limit;
> - int new_limit = ((old_limit + 1) << 4) - 1;
> - struct timer **newheap = xmalloc_array(struct timer *, new_limit +
> 1);
> + unsigned int old_limit = heap_metadata(heap)->limit;
> + unsigned int new_limit = ((old_limit + 1) << 4) - 1;
> + struct timer **newheap = NULL;
> +
> + /* Don't grow the heap beyond what is representable in its metadata.
> */
> + if ( new_limit == (typeof(heap_metadata(heap)->limit))new_limit &&
> + new_limit + 1 )
> + newheap = xmalloc_array(struct timer *, new_limit + 1);
It would probably be helpful to have a warn_once/print_once in the case
that we do hit the metadata limit
What is the new_limit + 1 for? Is it an overflow check?
Given a) that we're not moving from uint16_t while we have 32bit
hypervisor builds in use, and b) the calculation of new_limit will
truncate before getting into a position where this overflow check would
trip, I don't think it is helpful to retain.
~Andrew
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