Re: [PATCH] staging: fbtft: make dirty_lock IRQ-safe

[Nam Cao]

sh_def@xxxxxxx writes:
> diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
> index ca0c38221c16..193643d0329d 100644
> --- a/drivers/staging/fbtft/fbtft-core.c
> +++ b/drivers/staging/fbtft/fbtft-core.c
> @@ -298,14 +298,20 @@ static void fbtft_mkdirty(struct fb_info *info, int y, int height)
>  {
>  	struct fbtft_par *par = info->par;
>  	struct fb_deferred_io *fbdefio = info->fbdefio;
> +	unsigned long flags;
>  
>  	/* Mark display lines/area as dirty */
> -	spin_lock(&par->dirty_lock);
> +	/*
> +	 * fbcon takes dirty_lock while holding console_owner. Disable local
> +	 * interrupts here so a printk hardirq cannot acquire console_owner
> +	 * while dirty_lock is held and create the inverse lock ordering.
> +	 */

Beside that reason, we also need spin_lock_irqsave() because
fbtft_mkdirty() can be called in both task context and hardirq
context. And this reason alone suffices and usually is why
spin_lock_irqsave() is used, so I think a comment is not necessary.

But I am fine with it either way.

> +	spin_lock_irqsave(&par->dirty_lock, flags);
>  	if (y < par->dirty_lines_start)
>  		par->dirty_lines_start = y;
>  	if (y + height - 1 > par->dirty_lines_end)
>  		par->dirty_lines_end = y + height - 1;
> -	spin_unlock(&par->dirty_lock);
> +	spin_unlock_irqrestore(&par->dirty_lock, flags);
>  
>  	/* Schedule deferred_io to update display (no-op if already on queue)*/
>  	schedule_delayed_work(&info->deferred_work, fbdefio->delay);
> @@ -317,14 +323,15 @@ static void fbtft_deferred_io(struct fb_info *info, struct list_head *pagereflis
>  	unsigned int dirty_lines_start, dirty_lines_end;
>  	struct fb_deferred_io_pageref *pageref;
>  	unsigned int y_low = 0, y_high = 0;
> +	unsigned long flags;
>  
> -	spin_lock(&par->dirty_lock);
> +	spin_lock_irqsave(&par->dirty_lock, flags);
>  	dirty_lines_start = par->dirty_lines_start;
>  	dirty_lines_end = par->dirty_lines_end;
>  	/* set display line markers as clean */
>  	par->dirty_lines_start = par->info->var.yres - 1;
>  	par->dirty_lines_end = 0;
> -	spin_unlock(&par->dirty_lock);
> +	spin_unlock_irqrestore(&par->dirty_lock, flags);

fbtft_deferred_io() is executed in workqueue with interrupt enabled. So
it can use spin_lock_irq() instead of spin_lock_irqsave(), right?

Nam