linux-kernel - Re: [PATCH] omapfb: reduce stack usage

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Date:   Fri, 3 Jan 2020 13:50:40 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Ladislav Michl <ladis@...ux-mips.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH] omapfb: reduce stack usage


On 10/18/19 6:30 PM, Sudip Mukherjee wrote:
> The build of xtensa allmodconfig is giving a warning of:
> In function 'dsi_dump_dsidev_irqs':
> warning: the frame size of 1120 bytes is larger than 1024 bytes
> 
> Allocate the memory for 'struct dsi_irq_stats' dynamically instead
> of assigning it in stack.
> 
> Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>
> ---
>  drivers/video/fbdev/omap2/omapfb/dss/dsi.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/video/fbdev/omap2/omapfb/dss/dsi.c b/drivers/video/fbdev/omap2/omapfb/dss/dsi.c
> index d620376216e1..43402467bf40 100644
> --- a/drivers/video/fbdev/omap2/omapfb/dss/dsi.c
> +++ b/drivers/video/fbdev/omap2/omapfb/dss/dsi.c
> @@ -1536,22 +1536,25 @@ static void dsi_dump_dsidev_irqs(struct platform_device *dsidev,
>  {
>  	struct dsi_data *dsi = dsi_get_dsidrv_data(dsidev);
>  	unsigned long flags;
> -	struct dsi_irq_stats stats;
> +	struct dsi_irq_stats *stats;
>  
> +	stats = kmalloc(sizeof(*stats), GFP_KERNEL);
> +	if (!stats)
> +		return;
>  	spin_lock_irqsave(&dsi->irq_stats_lock, flags);
>  
> -	stats = dsi->irq_stats;
> +	memcpy(stats, &dsi->irq_stats, sizeof(*stats));

"stats" copy is only needed for generating debugfs information.

We can probably reduce the stack usage and also simplify the driver
by just accessing dsi->irq_stats directly before cleaning it
(we would also need to extend coverage of spinlock but the code is
debug only so this should not be a problem).

Care to try this approach?

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

>  	memset(&dsi->irq_stats, 0, sizeof(dsi->irq_stats));
>  	dsi->irq_stats.last_reset = jiffies;
>  
>  	spin_unlock_irqrestore(&dsi->irq_stats_lock, flags);
>  
>  	seq_printf(s, "period %u ms\n",
> -			jiffies_to_msecs(jiffies - stats.last_reset));
> +			jiffies_to_msecs(jiffies - stats->last_reset));
>  
> -	seq_printf(s, "irqs %d\n", stats.irq_count);
> +	seq_printf(s, "irqs %d\n", stats->irq_count);
>  #define PIS(x) \
> -	seq_printf(s, "%-20s %10d\n", #x, stats.dsi_irqs[ffs(DSI_IRQ_##x)-1]);
> +	seq_printf(s, "%-20s %10d\n", #x, stats->dsi_irqs[ffs(DSI_IRQ_##x)-1]);
>  
>  	seq_printf(s, "-- DSI%d interrupts --\n", dsi->module_id + 1);
>  	PIS(VC0);
> @@ -1575,10 +1578,10 @@ static void dsi_dump_dsidev_irqs(struct platform_device *dsidev,
>  
>  #define PIS(x) \
>  	seq_printf(s, "%-20s %10d %10d %10d %10d\n", #x, \
> -			stats.vc_irqs[0][ffs(DSI_VC_IRQ_##x)-1], \
> -			stats.vc_irqs[1][ffs(DSI_VC_IRQ_##x)-1], \
> -			stats.vc_irqs[2][ffs(DSI_VC_IRQ_##x)-1], \
> -			stats.vc_irqs[3][ffs(DSI_VC_IRQ_##x)-1]);
> +			stats->vc_irqs[0][ffs(DSI_VC_IRQ_##x)-1], \
> +			stats->vc_irqs[1][ffs(DSI_VC_IRQ_##x)-1], \
> +			stats->vc_irqs[2][ffs(DSI_VC_IRQ_##x)-1], \
> +			stats->vc_irqs[3][ffs(DSI_VC_IRQ_##x)-1]);
>  
>  	seq_printf(s, "-- VC interrupts --\n");
>  	PIS(CS);
> @@ -1594,7 +1597,7 @@ static void dsi_dump_dsidev_irqs(struct platform_device *dsidev,
>  
>  #define PIS(x) \
>  	seq_printf(s, "%-20s %10d\n", #x, \
> -			stats.cio_irqs[ffs(DSI_CIO_IRQ_##x)-1]);
> +			stats->cio_irqs[ffs(DSI_CIO_IRQ_##x)-1]);
>  
>  	seq_printf(s, "-- CIO interrupts --\n");
>  	PIS(ERRSYNCESC1);
> @@ -1618,6 +1621,7 @@ static void dsi_dump_dsidev_irqs(struct platform_device *dsidev,
>  	PIS(ULPSACTIVENOT_ALL0);
>  	PIS(ULPSACTIVENOT_ALL1);
>  #undef PIS
> +	kfree(stats);
>  }
>  
>  static void dsi1_dump_irqs(struct seq_file *s)