On Wed, Aug 28, 2013 at 07:48:14PM +0000, Christoph Lameter wrote: > Transformations done to __get_cpu_var() > > > 1. Determine the address of the percpu instance of the current processor. > > DEFINE_PER_CPU(int, y); > int *x = &__get_cpu_var(y); > > Converts to > > int *x = this_cpu_ptr(&y); > > > 2. Same as #1 but this time an array structure is involved. > > DEFINE_PER_CPU(int, y[20]); > int *x = __get_cpu_var(y); > > Converts to > > int *x = this_cpu_ptr(y); > > > 3. Retrieve the content of the current processors instance of a per cpu variable. > > DEFINE_PER_CPU(int, u); > int x = __get_cpu_var(y) > > Converts to > > int x = __this_cpu_read(y); > This looses a preemption debug check, so NAK > 4. Retrieve the content of a percpu struct > > DEFINE_PER_CPU(struct mystruct, y); > struct mystruct x = __get_cpu_var(y); > > Converts to > > memcpy(this_cpu_ptr(&x), y, sizeof(x)); > > 5. Assignment to a per cpu variable > > DEFINE_PER_CPU(int, y) > __get_cpu_var(y) = x; > > Converts to > > this_cpu_write(y, x); > This too looses a preemption debug check, NAK > 6. Increment/Decrement etc of a per cpu variable > > DEFINE_PER_CPU(int, y); > __get_cpu_var(y)++ > > Converts to > > this_cpu_inc(y) > Lo and behold.. no preemption checks again. Seriously first fix the debug and validation bits of the *this_cpu* stuff. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
