linux-kernel - Re: [PATCH v2] drm: use trace_printk rather than printk in drm

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Date:   Tue, 30 Jul 2019 23:26:32 -0700
From:   Joe Perches <joe@...ches.com>
To:     Fuqian Huang <huangfq.daxian@...il.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm: use trace_printk rather than printk in drm_dbg.

On Wed, 2019-07-31 at 14:24 +0800, Fuqian Huang wrote:
> In drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c,
> amdgpu_ih_process calls DRM_DEBUG which calls drm_dbg and
> finally calls printk.
> As amdgpu_ih_process is called from an interrupt handler,
> and interrupt handler should be short as possible.
> 
> As printk may lead to bogging down the system or can even
> create a live lock. printk should not be used in IRQ context.
> Instead, trace_printk is recommended in IRQ context.
> Link: https://lwn.net/Articles/365835
> 
> Reviewed-by: Joe Perches <joe@...ches.com> 

I made a suggestion.  I did not review this.

Please do not add signatures like this if
not specifically given by someone.


> Signed-off-by: Fuqian Huang <huangfq.daxian@...il.com>
> ---
> Changes in v2:
>   - Only make the interrupt uses the trace_printk to avoid
>     all 4000+ drm_dbg/DRM_DEBUG uses emitting a trace_printk.
> 
>  drivers/gpu/drm/drm_print.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> index a17c8a14dba4..747835d16fa6 100644
> --- a/drivers/gpu/drm/drm_print.c
> +++ b/drivers/gpu/drm/drm_print.c
> @@ -236,9 +236,13 @@ void drm_dbg(unsigned int category, const char *format, ...)
>  	vaf.fmt = format;
>  	vaf.va = &args;
>  
> -	printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> -	       __builtin_return_address(0), &vaf);
> -
> +	if (in_interrupt()) {
> +		trace_printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> +		       __builtin_return_address(0), &vaf);
> +	} else {
> +		printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> +		       __builtin_return_address(0), &vaf);
> +	}
>  	va_end(args);
>  }
>  EXPORT_SYMBOL(drm_dbg);