Messages in this thread | | | From | Rusty Russell <> | Subject | Dangerous code in cpumask_of_cpu? | Date | Tue, 8 Jul 2008 18:16:40 +1000 |
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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?
I don't know what the right answer is, but we might need to go to a pool of cpumask_ts, a get_cpumask_of_cpu() which can sleep and a put_cpumask_of_cpu?
Or maybe a gcc guru can refute this? Rusty.
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