Re: [PATCH v13 1/6] mm/vmstat: Add CPU-specific variable to track a vmstat discrepancy

[Christoph Lameter]

On Thu, 5 Jan 2023, Marcelo Tosatti wrote:

> +static inline void vmstat_mark_dirty(void)
> +{
> +	this_cpu_write(vmstat_dirty, true);
> +}

this_cpu_write() is intended for an per cpu atomic context. You are not
using it in that way. The processor may have changed before or after and
thus vmstat_dirty for another CPU may  have been marked dirty.

I guess this would have to be called __vmstat_mark_dirty() and be using
__this_cpu_write(*) with a requirement that preemption be disabled before
using this function.

> +static inline void vmstat_clear_dirty(void)
> +{
> +	this_cpu_write(vmstat_dirty, false);
> +}

Same

> +static inline bool is_vmstat_dirty(void)
> +{
> +	return this_cpu_read(vmstat_dirty);
> +}

This function would only work correctly if preemption is disabled.
Otherwise the processor may change.