Re: [PATCH] zsmalloc: do not use bit_spin_lock

[Mike Galbraith]

On Sun, 2020-12-20 at 02:22 +0200, Vitaly Wool wrote:
> zsmalloc takes bit spinlock in its _map() callback and releases it
> only in unmap() which is unsafe and leads to zswap complaining
> about scheduling in atomic context.
>
> To fix that and to improve RT properties of zsmalloc, remove that
> bit spinlock completely and use a bit flag instead.


> -static void pin_tag(unsigned long handle) __acquires(bitlock)
> +static void pin_tag(unsigned long handle)
>  {
> -	bit_spin_lock(HANDLE_PIN_BIT, (unsigned long *)handle);
> +	preempt_disable();
> +	while(test_and_set_bit(HANDLE_PIN_BIT, (unsigned long *)handle))
> +		cpu_relax();
> +	preempt_enable();
>  }

If try doesn't need to disable preemption, neither does pin.

	-Mike