Re: [PATCH v2 2/2] writeback: Rework wb_[dec|inc]_stat family of functions

From: Tejun Heo
Date: Tue Jun 20 2017 - 15:37:32 EST

Hello, Nikolay.

On Tue, Jun 20, 2017 at 09:02:00PM +0300, Nikolay Borisov wrote:
> Currently the writeback statistics code uses a percpu counters to hold
> various statistics. Furthermore we have 2 families of functions - those which
> disable local irq and those which doesn't and whose names begin with
> double underscore. However, they both end up calling __add_wb_stats which in
> turn calls percpu_counter_add_batch which is already irq-safe.

Heh, looks like I was confused. __percpu_counter_add() is not
irq-safe. It disables preemption and uses __this_cpu_read(), so
there's no protection against irq. If writeback statistics want
irq-safe operations and it does, it would need these separate
operations. Am I missing something?