Re: [PATCH 1/2] mm/page_owner: Introduce SNPRINTF() macro that includes length error check

[Waiman Long <longman@xxxxxxxxxx>]

On 1/28/22 16:18, Ira Weiny wrote:
> On Fri, Jan 28, 2022 at 02:56:41PM -0500, Waiman Long wrote:
> > In print_page_owner(), there is a repetitive check after each snprintf()
> > to make sure that the final length is less than the buffer size. Simplify
> > the code and make it easier to read by embedding the buffer length
> > check and increment inside the macro.
> This does not follow the kernel coding style of not putting control flow
> statements in macros.[1]

OK, fair enough. I can remove the macro and repost the patch.

Cheers,
Longman

> > Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> > ---
> >   mm/page_owner.c | 50 +++++++++++++++++++++++--------------------------
> >   1 file changed, 23 insertions(+), 27 deletions(-)
> And in the end you only saved 4 lines of code to read...  Not worth it IMO.
>
> Ira
>
> [1] https://www.kernel.org/doc/html/v4.17/process/coding-style.html
>
> > diff --git a/mm/page_owner.c b/mm/page_owner.c
> > index 99e360df9465..c52ce9d6bc3b 100644
> > --- a/mm/page_owner.c
> > +++ b/mm/page_owner.c
> > @@ -325,12 +325,20 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
> >   	seq_putc(m, '\n');
> >   }
> >   
> > +#define SNPRINTF(_buf, _size, _len, _err, _fmt, ...)			\
> > +	do {								\
> > +		_len += snprintf(_buf + _len, _size - _len, _fmt,	\
> > +				 ##__VA_ARGS__);			\
> > +		if (_len >= _size)					\
> > +			goto _err;					\
> > +	} while (0)
> > +
> >   static ssize_t
> >   print_page_owner(char __user *buf, size_t count, unsigned long pfn,
> >   		struct page *page, struct page_owner *page_owner,
> >   		depot_stack_handle_t handle)
> >   {
> > -	int ret, pageblock_mt, page_mt;
> > +	int ret = 0, pageblock_mt, page_mt;
> >   	char *kbuf;
> >   
> >   	count = min_t(size_t, count, PAGE_SIZE);
> > @@ -338,44 +346,32 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
> >   	if (!kbuf)
> >   		return -ENOMEM;
> >   
> > -	ret = snprintf(kbuf, count,
> > -			"Page allocated via order %u, mask %#x(%pGg), pid %d, ts %llu ns, free_ts %llu ns\n",
> > -			page_owner->order, page_owner->gfp_mask,
> > -			&page_owner->gfp_mask, page_owner->pid,
> > -			page_owner->ts_nsec, page_owner->free_ts_nsec);
> > -
> > -	if (ret >= count)
> > -		goto err;
> > +	SNPRINTF(kbuf, count, ret, err,
> > +		"Page allocated via order %u, mask %#x(%pGg), pid %d, ts %llu ns, free_ts %llu ns\n",
> > +		page_owner->order, page_owner->gfp_mask,
> > +		&page_owner->gfp_mask, page_owner->pid,
> > +		page_owner->ts_nsec, page_owner->free_ts_nsec);
> >   
> >   	/* Print information relevant to grouping pages by mobility */
> >   	pageblock_mt = get_pageblock_migratetype(page);
> >   	page_mt  = gfp_migratetype(page_owner->gfp_mask);
> > -	ret += snprintf(kbuf + ret, count - ret,
> > -			"PFN %lu type %s Block %lu type %s Flags %pGp\n",
> > -			pfn,
> > -			migratetype_names[page_mt],
> > -			pfn >> pageblock_order,
> > -			migratetype_names[pageblock_mt],
> > -			&page->flags);
> > -
> > -	if (ret >= count)
> > -		goto err;
> > +	SNPRINTF(kbuf, count, ret, err,
> > +		"PFN %lu type %s Block %lu type %s Flags %pGp\n",
> > +		pfn, migratetype_names[page_mt],
> > +		pfn >> pageblock_order,
> > +		migratetype_names[pageblock_mt],
> > +		&page->flags);
> >   
> >   	ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
> >   	if (ret >= count)
> >   		goto err;
> >   
> > -	if (page_owner->last_migrate_reason != -1) {
> > -		ret += snprintf(kbuf + ret, count - ret,
> > +	if (page_owner->last_migrate_reason != -1)
> > +		SNPRINTF(kbuf, count, ret, err,
> >   			"Page has been migrated, last migrate reason: %s\n",
> >   			migrate_reason_names[page_owner->last_migrate_reason]);
> > -		if (ret >= count)
> > -			goto err;
> > -	}
> >   
> > -	ret += snprintf(kbuf + ret, count - ret, "\n");
> > -	if (ret >= count)
> > -		goto err;
> > +	SNPRINTF(kbuf, count, ret, err, "\n");
> >   
> >   	if (copy_to_user(buf, kbuf, ret))
> >   		ret = -EFAULT;
> > --
> > 2.27.0