linux-kernel - Re: [Bug #12409] NULL pointer dereference at get

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Date:	Wed, 11 Feb 2009 15:02:08 -0800
From:	Alok Kataria <akataria@...are.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	"frederik.deweerdt@...og.eu" <frederik.deweerdt@...og.eu>,
	"rjw@...k.pl" <rjw@...k.pl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kernel-testers@...r.kernel.org" <kernel-testers@...r.kernel.org>,
	Daniel Hecht <dhecht@...are.com>
Subject: Re: [Bug #12409] NULL pointer dereference at get_stats()

On Wed, 2009-02-11 at 14:54 -0800, Alok Kataria wrote:
> Hi Tetsuo,
> 
> Thanks for reporting this. Yes i tried it here with a slightly
> different .config and i did see the problem. I will try to figure out
> what is happening over here, but before doing that let me ask if this
> bug is only in the stable series ? 
> Do we know for which kernel does the "nolapic" option doesn't hit this
> bug ? 
> 
> Also, I assume its not present in 2.6.29-rc ?

Okay i went through the whole thread, and notice that all of my queries
were previously answered. 

And what happened to this patch of checking the stats only if its not
null.

+if (!lb_stats) {
+			printk(KERN_INFO "lb_stats == NULL for CPU %u\n", i);
+			continue;
+
		}
> 
> Thanks,
> Alok
> 
> On Mon, 2009-02-09 at 03:19 -0800, Tetsuo Handa wrote:
> > Hello.
> > 
> > > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=12409
> > > Subject		: NULL pointer dereference at get_stats()
> > > Submitter	: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> > > Date		: 2008-12-30 12:53 (21 days old)
> > > References	: http://marc.info/?l=linux-kernel&m=123064167008695&w=4
> > > Handled-By	: Frederik Deweerdt <frederik.deweerdt@...og.eu>
> > 
> > I made custom initramfs and tested on native environment and KVM and VMware.
> > This problem happened only in VMware.
> > 
> > Alok and Daniel (cc: added), can you reproduce this problem?
> > 
> > Problem description:
> > 
> >   Compiling 2.6.28.4 using config at http://I-love.SAKURA.ne.jp/tmp/config-2.6.28-bug
> >   and booting with "nolapic" option on x86 machine with 2 CPUs, NULL pointer
> >   dereference happens at get_stats() because for_each_possible_cpu() reaches
> >   CPU 1 while "nolapic" option should prevent for_each_possible_cpu() from
> >   reaching CPU 1.
> > 
> >   Compiling 2.6.28.4 using config at http://I-love.SAKURA.ne.jp/tmp/config-2.6.28-nobug
> >   (all options in "Power management and ACPI options" section disabled)
> >   solves this problem.
> > 
> >   Also, this problem seems to be VMware specific.
> >   I couldn't reproduce this problem on native environment and KVM.
> > 
> > Native environment (no problem):
> > 
> >   CentOS 5.2 (x86_64) and Ubuntu 8.04 (i386) on ThinkPad X60
> > 
> > KVM environment (no problem):
> > 
> >   kvm -kernel /boot/vmlinuz-2.6.28.4 -initrd /boot/init -net none -hda /var/tmp/image.img -vnc xx.xx.xx.xx:0 --append "ro nolapic" -smp 2
> >   on Ubuntu 8.04 (i386) on ThinkPad X60
> > 
> > VMware environment (problematic):
> > 
> >   Debian Sarge (i386) / CentOS 5.2 (i386) on VMware workstation 6.5.1 (x86_64)
> >   on CentOS 5.2 (x86_64) on ThinkPad X60
> > 
> > Problematic kernel versions:
> > 
> >   2.6.27.x and 2.6.28.x .
> > 
> > Regards.
> > 
> > ----- Custom initramfs -----
> > /*
> >   gcc -Wall -O3 -static -o init init.c
> >   echo init | cpio -o -H newc | gzip -9 > /boot/init
> >  */
> > #include <sys/mount.h>
> > #include <sys/types.h>
> > #include <sys/stat.h>
> > #include <fcntl.h>
> > #include <unistd.h>
> > #include <stdio.h>
> > #include <string.h>
> > 
> > int main(int argc, char *argv[]) {
> > 	FILE *fp;
> > 	char buffer[1024];
> > 	memset(buffer, 0, sizeof(buffer));
> > 	mkdir("/proc", 0755);
> > 	mount("none", "/proc", "proc", 0, NULL);
> > 	fp = fopen("/proc/cpuinfo", "r");
> > 	while (fgets(buffer, sizeof(buffer) - 1, fp))
> > 		if (strstr(buffer, "processor"))
> > 			printf("%s", buffer);
> > 	fclose(fp);
> > 	fp = fopen("/proc/cmdline", "r");
> > 	fgets(buffer, sizeof(buffer) - 1, fp);
> > 	fclose(fp);
> > 	printf("%s", buffer);
> > 	fflush(stdout);
> > 	if (mkdir("/sys", 0755) || mount("/sys/", "/sys/", "sysfs", 0, NULL)) {
> > 		printf("mount failed\n");
> > 		while (1)
> > 			sleep(1);
> > 	}
> > 	fp = fopen("/sys/class/net/lo/statistics/rx_packets", "r");
> > 	if (!fp) {
> > 		printf("open failed\n");
> > 		while (1)
> > 			sleep(1);
> > 	}
> > 	while (fgets(buffer, sizeof(buffer) - 1, fp))
> > 		;
> > 	fclose(fp);
> > 	printf("done\n");
> > 	while (1)
> > 		sleep(1);
> > 	return 0;
> > }

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