Messages in this thread | | | From | Johannes Weiner <> | Subject | Re: Dangerous code in cpumask_of_cpu? | Date | Tue, 08 Jul 2008 10:35:20 +0200 |
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Hi,
Rusty Russell <rusty@rustcorp.com.au> writes:
> Hi Christoph/Mike, > > Looked at cpumask_of_cpu as introduced in > 9f0e8d0400d925c3acd5f4e01dbeb736e4011882 (x86: convert cpumask_of_cpu macro > to allocated array), and I don't think it's safe: > > #define cpumask_of_cpu(cpu) \ > (*({ \ > typeof(_unused_cpumask_arg_) m; \ > if (sizeof(m) == sizeof(unsigned long)) { \ > m.bits[0] = 1UL<<(cpu); \ > } else { \ > cpus_clear(m); \ > cpu_set((cpu), m); \ > } \ > &m; \ > })) > > Referring to &m once out of scope is invalid, and I can't find any evidence > that it's legal here. In particular, the change > b53e921ba1cff8453dc9a87a84052fa12d5b30bd (generic: reduce stack pressure in > sched_affinity) which passes &m to other functions seems highly risky. > > I'm surprised this hasn't already hit us, but perhaps gcc isn't as clever as > it could be?
You don't refer to &m outside scope. Look at the character below the first e of #define :)
But then, this code should probably just evaluate to m without this obscure *(&m) construct.
Hannes
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