On 12/13, Srivatsa S. Bhat wrote: > > On 12/13/2012 09:47 PM, Oleg Nesterov wrote: > > On 12/13, Srivatsa S. Bhat wrote: > >> > >> On 12/13/2012 12:42 AM, Srivatsa S. Bhat wrote: > >>> > >>> Even I don't spot anything wrong with it. But I'll give it some more > >>> thought.. > >> > >> Since an interrupt handler can also run get_online_cpus_atomic(), we > >> cannot use the __this_cpu_* versions for modifying reader_percpu_refcnt, > >> right? > > > > Hmm. I thought that __this_cpu_* must be safe under preempt_disable(). > > IOW, I thought that, say, this_cpu_inc() is "equal" to preempt_disable + > > __this_cpu_inc() correctness-wise. > > > > And. I thought that this_cpu_inc() is safe wrt interrupt, like local_t. > > > > But when I try to read the comments percpu.h, I am starting to think that > > even this_cpu_inc() is not safe if irq handler can do the same? > > > > The comment seems to say that its not safe wrt interrupts. But looking at > the code in include/linux/percpu.h, IIUC, that is true only about > this_cpu_read() because it only disables preemption. > > However, this_cpu_inc() looks safe wrt interrupts because it wraps the > increment within raw_local_irqsave()/restore().
You mean _this_cpu_generic_to_op() I guess. So yes, I think you are right, this_cpu_* should be irq-safe, but __this_cpu_* is not. Thanks. At least on x86 there is no difference between this_ and __this_, both do percpu_add_op() without local_irq_disable/enable. But it seems that most of architectures use generic code. Oleg. -- 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/
