* Re: [Bug 204371] BUG kmalloc-4k (Tainted: G W ): Object padding overwritten
[not found] ` <bug-204371-206035-O9m4mwJN9f@https.bugzilla.kernel.org/>
@ 2019-08-17 8:09 ` christophe leroy
0 siblings, 0 replies; only message in thread
From: christophe leroy @ 2019-08-17 8:09 UTC (permalink / raw)
To: bugzilla-daemon, linuxppc-dev, Andrew Morton,
Linux Memory Management List, linux-btrfs, erhard_f, Chris Mason,
Josef Bacik, David Sterba, Michael Ellerman
Le 30/07/2019 à 20:52, bugzilla-daemon@bugzilla.kernel.org a écrit :
> https://bugzilla.kernel.org/show_bug.cgi?id=204371
>
> --- Comment #2 from Andrew Morton (akpm@linux-foundation.org) ---
> (switched to email. Please respond via emailed reply-to-all, not via the
> bugzilla web interface).
Reply all replies to bugzilla-daemon@bugzilla.kernel.org only.
[...]
>
> cc'ing various people here.
Hum ... only got that email through the bugzilla interface, and CC'ed
people don't show up.
>
> I suspect proc_cgroup_show() is innocent and that perhaps
> bpf_prepare_filter() had a memory scribble. iirc there has been at
> least one recent pretty serious bpf fix applied recently. Can others
> please take a look?
>
> (Seriously - please don't modify this report via the bugzilla web interface!)
>
Haven't got the original CC'ed list, so please reply with missing Cc's
if any.
We have well progressed on this case.
Erhard made a relation being this "Object padding overwritten" issue
arising on any driver, and the presence of the BTRFS driver.
Then he was able to bisect the issue to:
commit 69d2480456d1baf027a86e530989d7bedd698d5f
Author: David Sterba <dsterba@suse.com>
Date: Fri Jun 29 10:56:44 2018 +0200
btrfs: use copy_page for copying pages instead of memcpy
Use the helper that's possibly optimized for full page copies.
Signed-off-by: David Sterba <dsterba@suse.com>
After looking in the code, it has appeared that some of the said "pages"
were allocated with "kzalloc()".
Using the patch https://patchwork.ozlabs.org/patch/1148033/ Erhard
confirmed that some btrfs functions were calling copy_page() with
misaligned destinations.
copy_page(), at least on powerpc, expects cache aligned destination.
The patch https://patchwork.ozlabs.org/patch/1148606/ fixes the issue.
Christophe
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