linux-kernel - Re: [PATCH] mm: Fix printk format strings

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Date:	Thu, 11 Oct 2007 09:04:57 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Nick Piggin" <nickpiggin@...oo.com.au>,
	"Hugh Dickins" <hugh@...itas.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Fix printk format strings

On 10/11/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Thu, 11 Oct 2007 08:47:01 +0200 Vegard Nossum <vegard.nossum@...il.com> wrote:
>
> > This makes sure printk format strings contain no more than a single
> > line.
> >
> > Signed-off-by: Vegard Nossum <vegard.nossum@...il.com>
> > ---
> >  mm/page_alloc.c |   20 +++++++++++---------
> >  1 files changed, 11 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 1a8c595..96f0b33 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -198,13 +198,15 @@ static inline int bad_range(struct zone *zone, struct page *page)
> >
> >  static void bad_page(struct page *page)
> >  {
> > -     printk(KERN_EMERG "Bad page state in process '%s'\n"
> > -             KERN_EMERG "page:%p flags:0x%0*lx mapping:%p mapcount:%d count:%d\n"
> > -             KERN_EMERG "Trying to fix it up, but a reboot is needed\n"
> > -             KERN_EMERG "Backtrace:\n",
> > -             current->comm, page, (int)(2*sizeof(unsigned long)),
> > -             (unsigned long)page->flags, page->mapping,
> > +     printk(KERN_EMERG "Bad page state in process '%s'\n", current->comm);
> > +     printk(KERN_EMERG
> > +             "page:%p flags:0x%0*lx mapping:%p mapcount:%d count:%d\n",
> > +             page, (int) (2 * sizeof(unsigned long)),
> > +             (unsigned long) page->flags, page->mapping,
> >               page_mapcount(page), page_count(page));
> > +     printk(KERN_EMERG "Trying to fix it up, but a reboot is needed\n");
> > +     printk(KERN_EMERG "Backtrace:\n");
> > +
> >       dump_stack();
> >       page->flags &= ~(1 << PG_lru    |
> >                       1 << PG_private |
> > @@ -1575,13 +1577,13 @@ void show_free_areas(void)
> >               }
> >       }
> >
> > -     printk("Active:%lu inactive:%lu dirty:%lu writeback:%lu unstable:%lu\n"
> > -             " free:%lu slab:%lu mapped:%lu pagetables:%lu bounce:%lu\n",
> > +     printk("Active:%lu inactive:%lu dirty:%lu writeback:%lu unstable:%lu\n",
> >               global_page_state(NR_ACTIVE),
> >               global_page_state(NR_INACTIVE),
> >               global_page_state(NR_FILE_DIRTY),
> >               global_page_state(NR_WRITEBACK),
> > -             global_page_state(NR_UNSTABLE_NFS),
> > +             global_page_state(NR_UNSTABLE_NFS));
> > +     printk(" free:%lu slab:%lu mapped:%lu pagetables:%lu bounce:%lu\n",
> >               global_page_state(NR_FREE_PAGES),
> >               global_page_state(NR_SLAB_RECLAIMABLE) +
> >                       global_page_state(NR_SLAB_UNRECLAIMABLE),
>
> I don't understand the reason for this change.

I'm sorry :). It helps to make one line per call only, since this
allows changing the printk internals for the better by reducing some
complexity. I believe this is a good thing. I have a patch that
changes printk, but it assumes that each format string only contains a
single line. Is this a very bad assumption to make? Or maybe I should
have sent that change first and made a reference to it?

But don't you also agree, on the grounds of principle, that a single
line per call is better style?

Vegard
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