Re: [linux-pm] OOPS: divide error while s2dsk (2.6.20-rc1-mm1)

[Andrew Morton]

On Mon, 18 Dec 2006 18:02:20 +0100
Jiri Slaby <jirislaby@xxxxxxxxx> wrote:

> Rafael J. Wysocki wrote:
> > Hi,
> > 
> > On Monday, 18 December 2006 12:20, Jiri Slaby wrote:
> >> Hi.
> >>
> >> I got this oops while suspending:
> >> [  309.366557] Disabling non-boot CPUs ...
> >> [  309.386563] CPU 1 is now offline
> >> [  309.387625] CPU1 is down
> >> [  309.387704] Stopping tasks ... done.
> >> [  310.030991] Shrinking memory... -<0>divide error: 0000 [#1]
> >> [  310.456669] SMP
> >> [  310.456814] last sysfs file:
> >> /devices/pci0000:00/0000:00:1e.0/0000:02:08.0/eth0/statistics/collisions
> >> [  310.456919] Modules linked in: eth1394 floppy ohci1394 ide_cd ieee1394 cdrom
> >> [  310.457259] CPU:    0
> >> [  310.457260] EIP:    0060:[<c0150c9a>]    Not tainted VLI
> >> [  310.457261] EFLAGS: 00210246   (2.6.20-rc1-mm1 #207)
> >> [  310.457478] EIP is at shrink_slab+0x9e/0x169
> > 
> > Looks like we have a problem with slab shrinking here.
> > 
> > Could you please use gdb to check what exactly is at shrink_slab+0x9e?
> 
> Sure, but not till Friday, sorry (I am away).

I think there's only one divide in there which can do this, so...

--- a/mm/vmscan.c~shrink_slab-handle-bad-shrinkers
+++ a/mm/vmscan.c
@@ -20,6 +20,7 @@
 #include <linux/pagemap.h>
 #include <linux/init.h>
 #include <linux/highmem.h>
+#include <linux/kallsyms.h>
 #include <linux/vmstat.h>
 #include <linux/file.h>
 #include <linux/writeback.h>
@@ -190,7 +191,13 @@ unsigned long shrink_slab(unsigned long 
 		unsigned long total_scan;
 		unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask);
 
-		delta = (4 * scanned) / shrinker->seeks;
+		if (!shrinker->seeks) {
+			print_symbol("shrinker %s has zero seeks\n",
+				(unsigned long)shrinker->shrinker);
+			delta = (4 * scanned) / DEFAULT_SEEKS;
+		} else {
+			delta = (4 * scanned) / shrinker->seeks;
+		}
 		delta *= max_pass;
 		do_div(delta, lru_pages + 1);
 		shrinker->nr += delta;
_

A quick grep shows that all set_shrinker() callers are doing the right
thing, so something kooky has happened.

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