Hi Ingo, On 12/03/2015 at 04:28 PM, Ingo Molnar wrote: > * Xunlei Pang <[email protected]> wrote: > >> Hi Peter, >> >> On 12/03/2015 at 12:25 AM, Peter Zijlstra wrote: >>> On Wed, Dec 02, 2015 at 09:12:30PM +0800, Xunlei Pang wrote: >>>> Hi Peter, >>>> >>>> On 12/02/2015 at 08:34 PM, Peter Zijlstra wrote: >>>>> On Wed, Dec 02, 2015 at 07:52:59PM +0800, Xunlei Pang wrote: >>>>>> The patch cleans the garbage by using zalloc_cpumask_var() >>>>>> instead of alloc_cpumask_var() for root_domain::rto_mask >>>>>> allocation, thereby addressing the issues. >>>>> How did you notice this? Also do we want to do the same for the kmalloc >>>> When doing review. >>> Nice, will you be looking for similar issues elsewhere in the scheduler >>> too? >> Sure :-) > Hm, is the alloc_cpumask_var() done in alloc_sched_domains() safe?
Until now, I haven't found any other similar issues, but I will check further. > > At least the usage pattern in init_sched_domains() looks unsafe: > > doms_cur = alloc_sched_domains(ndoms_cur); > if (!doms_cur) > doms_cur = &fallback_doms; > cpumask_andnot(doms_cur[0], cpu_map, cpu_isolated_map); > > I think alloc_cpumask_var() is a fundamentally unsafe or at least fragile > operation, because the uninitialized variable bug will only happen on large > CPU > count kernels AFAICS - so it's inviting such bugs. > > How about we rename alloc_cpumask_var() to alloc_cpumask_var_noinit() or at > least > __alloc_cpumask_var(), to make this property easier to see? There have already been many call sites of it in the kernel, at least we still have zalloc_cpumask_var(), maybe we could add some function comments, reminding people of thinking of zalloc_cpumask_var() for their cases. Regards, Xunlei > > Thanks, > > Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
