[PATCH] mm: Fix printk format strings

[PATCH] mm: Fix printk format strings

[Vegard Nossum]

This makes sure printk format strings contain no more than a single
line.

Signed-off-by: Vegard Nossum <vegard.nossum@gmail.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),
-- 
1.5.2.4

Re: [PATCH] mm: Fix printk format strings

[Andrew Morton]

On Thu, 11 Oct 2007 08:47:01 +0200 Vegard Nossum <vegard.nossum@gmail.com> wrote:

> This makes sure printk format strings contain no more than a single
> line.
> 
> Signed-off-by: Vegard Nossum <vegard.nossum@gmail.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.

Re: [PATCH] mm: Fix printk format strings

[Vegard Nossum]

On 10/11/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 11 Oct 2007 08:47:01 +0200 Vegard Nossum <vegard.nossum@gmail.com> wrote:
>
> > This makes sure printk format strings contain no more than a single
> > line.
> >
> > Signed-off-by: Vegard Nossum <vegard.nossum@gmail.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

Re: [PATCH] mm: Fix printk format strings

[Andrew Morton]

On Thu, 11 Oct 2007 09:04:57 +0200 "Vegard Nossum" <vegard.nossum@gmail.com> wrote:

> > > -     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?

Well we do multiple-lines-per-printk in rather a lot of places and it has
two advantages:

- less text size (I expect)

- the printk is "atomic" in that the logically-connected output lines
  won't get tangled up with an intervening printk from another CPU, or from
  an interrupt handler on this CPU.

Those are pretty modest advantages and I guess we could live without them
if we got a significant gain from doing so.  But it'd take quite some
effort hunting down all the callsites, and preventing new ones from
occuring.

Re: [PATCH] mm: Fix printk format strings

[Vegard Nossum]

On 10/11/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 11 Oct 2007 09:04:57 +0200 "Vegard Nossum" <vegard.nossum@gmail.com> wrote:
>
> > > > -     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?
>
> Well we do multiple-lines-per-printk in rather a lot of places and it has
> two advantages:
>
> - less text size (I expect)
>
> - the printk is "atomic" in that the logically-connected output lines
>   won't get tangled up with an intervening printk from another CPU, or from
>   an interrupt handler on this CPU.
>
> Those are pretty modest advantages and I guess we could live without them
> if we got a significant gain from doing so.  But it'd take quite some
> effort hunting down all the callsites, and preventing new ones from
> occuring.

I have written a sparse program to detect all callers that don't use
single-line literal strings for the printk format (posted to sparse
mailing list yesterday). So in fact, what I was doing was just that,
hunting them down and cleaning it up.

It so happens that my other patch also introduce a buffered printk
that supports atomic line continuations and multiple uninterrupted
lines, though this requires of course that the callers use these
functions. Other benefits include writing directly to the ring-buffer,
saving a 1K temporary buffer. The printk patch(es) can be viewed at
http://folk.uio.no/vegardno/xprintf/

Vegard