linux-kernel - Re: [PATCH v22 2/5] ring-buffer: Introducing ring-buffer mapping functions

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Date: Fri, 10 May 2024 12:03:12 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, mhiramat@...nel.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	mathieu.desnoyers@...icios.com, kernel-team@...roid.com,
	rdunlap@...radead.org, rppt@...nel.org, linux-mm@...ck.org
Subject: Re: [PATCH v22 2/5] ring-buffer: Introducing ring-buffer mapping
 functions

[...]

> > > +
> > > +	while (s < nr_subbufs && p < nr_pages) {
> > > +		struct page *page = virt_to_page(cpu_buffer->subbuf_ids[s]);
> > > +		int off = 0;
> > > +
> > > +		for (; off < (1 << (subbuf_order)); off++, page++) {
> > > +			if (p >= nr_pages)
> > > +				break;
> > > +
> > > +			pages[p++] = page;
> > > +		}
> > > +		s++;
> > > +	}
> > 
> > The above can be made to:
> > 
> > 	while (p < nr_pages) {
> > 		struct page *page;
> > 		int off = 0;
> > 
> > 		if (WARN_ON_ONCE(s >= nr_subbufs))
> > 			break;
> 
> I'm not particularly happy about us calling vm_insert_pages with NULL
> pointers stored in pages.
> 
> Should we instead do
> 
> if (WARN_ON_ONCE(s >= nr_subbufs)) {
> 	err = -EINVAL;
> 	goto out;
> }
> 
> ?

I could also nr_pages = p in the event of s >= nr_subbufs... but that
really that shouldn't happen so let's return an error.

> 
> -- 
> Cheers,
> 
> David / dhildenb
>