linux-kernel - Re: [PATCH 3/3] printk: dump full information of page flags in pGp

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Message-ID: <YBKp/NHanaN4e0im@smile.fi.intel.com>
Date:   Thu, 28 Jan 2021 14:11:40 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     david@...hat.com, vbabka@...e.cz, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, pmladek@...e.com, rostedt@...dmis.org,
        sergey.senozhatsky@...il.com, linux@...musvillemoes.dk,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] printk: dump full information of page flags in pGp

On Thu, Jan 28, 2021 at 10:19:47AM +0800, Yafang Shao wrote:
> Currently the pGp only shows the names of page flags, rather than
> the full information including section, node, zone, last cpupid and
> kasan tag. While it is not easy to parse these information manually
> because there're so many flavors. Let's interpret them in pGp as well.
> 
> - Before the patch,
> [ 6312.639698] ERR: Slab 0x000000006d1133b9 objects=33 used=3 fp=0x000000006d0779d1 flags=0x17ffffc0010200(slab|head)
> 
> - After the patch,
> [ 6315.235783] ERR: Slab 0x000000006d1133b9 objects=33 used=3 fp=0x000000006d0779d1 flags=0x17ffffc0010200(Node 0x0,Zone 0x2,Lastcpupid 0x1fffff,slab|head)

> +	int i;
> +
> +	for (i = 0; i < sizeof(pfl) / sizeof(struct page_flags_layout) && buf < end; i++) {

'buf < end' is redundant.

> +		if (pfl[i].width == 0)
> +			continue;
> +
> +		buf = string(buf, end, pfl[i].name, default_str_spec);

> +		if (buf >= end)
> +			break;

Can you rather use usual patter, i.e.

	if (buf < end) {
		...do something...
	}
	buf++; // or whatever increase should be done

Moreover, number() and string() IIRC have the proper checks embedded into them.

> +		buf = number(buf, end, (flags >> pfl[i].shift) & pfl[i].mask,
> +			     default_flag_spec);

> +		if (buf >= end)
> +			break;
> +		*buf = ',';
> +		buf++;

Here is a very standard pattern can be used, see code around

		if (buf < end)
			*buf = ',';
		buf++;

> +	}

-- 
With Best Regards,
Andy Shevchenko