Re: BUG: Bad page map in process udevd (anon_vma: (null)) in 2.6.38-rc4

On Thu 17-02-11 08:13:50, Linus Torvalds wrote:

On Thu, Feb 17, 2011 at 1:09 AM, Michal Hocko [off-list ref] wrote:

quoted

I have seen that thread but I didn't think it is related. I thought
this is an another anon_vma issue. But you seem to be right that the
offset pattern can be related.

Hey, maybe it turns out to be about anon_vma's in the end, but I see
no big reason to blame them per se. And we haven't had all that much
churn wrt anon_vma's this release window, so I wouldn't expect
anything exciting unless you're actively using transparent hugepages.
And iirc, Eric was not using them (or memory compaction).

I am using transparent hugepages:
$ grep -i huge /proc/vmstat 
nr_anon_transparent_hugepages 24

and this is the usual number that I can see with my day-to-day workload.

I'd be more likely to blame either the new path lookup (which uses
totally new RCU freeing of inodes _and_
INIT_LIST_HEAD(&inode->i_dentry)), but I'm not seeing how that could
break either (I've gone through that patch many times).

And in addition, I don't see why others wouldn't see it (I've got
DEBUG_PAGEALLOC and SLUB_DEBUG_ON turned on myself, and I know others
do too).

So I'm wondering what triggers it. Must be something subtle.

quoted

OK. I have just booted with the same kernel and the config turned on.
Let's see if I am able to reproduce.

Thanks. It might have been good to turn on SLUB_DEBUG_ON and
DEBUG_LIST too, but PAGEALLOC is the big one.

I can try those later as well. Currently I am not able to trigger the
issue. I am running rmmod wireless stack + modproble it back in the loop
because this was the last thing before I saw the bug last time. Let's
see if it changes later.

quoted

Btw.
$ objdump -d ./vmlinux-2.6.38-rc4-00001-g07409af-vmscan-test | grep 0x1e68

didn't print out anything. Do you have any other way to find out the
structure?

Nope, that's roughly what I did to (in addition to doing all the .ko
files and checking for 0xe68 too). 

Ohh, I forgot about modules. Just did it and also nothing found.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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