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Subject: Re: [PATCH v5 2/7] slob: Respect list_head abstraction layer
To:     "Tobin C. Harding" <me@tobin.cc>, Roman Gushchin <guro@fb.com>
Cc:     "Tobin C. Harding" <tobin@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
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        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Matthew Wilcox <willy@infradead.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <63e395fc-41c5-00bf-0767-a313554f7b23@suse.cz>
Date:   Tue, 9 Apr 2019 14:59:52 +0200
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On 4/3/19 11:13 PM, Tobin C. Harding wrote:

> According to 0day test robot this is triggering an error from
> CHECK_DATA_CORRUPTION when the kernel is built with CONFIG_DEBUG_LIST.

FWIW, that report [1] was for commit 15c8410c67adef from next-20190401. I've
checked and it's still the v4 version, although the report came after you
submitted v5 (it wasn't testing the patches from mailing list, but mmotm). I
don't see any report for the v5 version so I'd expect it to be indeed fixed by
the new approach that adds boolean return parameter to slob_page_alloc().

Vlastimil

[1] https://lore.kernel.org/linux-mm/5ca413c6.9TM84kwWw8lLhnmK%25lkp@intel.com/T/#u

> I think this is because list_rotate_to_front() puts the list into an
> invalid state before it calls __list_add().  The thing that has me
> stumped is why this was not happening before this patch series was
> applied?  ATM I'm not able to get my test module to trigger this but I'm
> going to try a bit harder today.  If I'm right one solution is to modify
> list_rotate_to_front() to _not_ call __list_add() but do it manually,
> this solution doesn't sit well with me though.
> 
> So, summing up, I think the patch is correct in that it does the correct
> thing but I think the debugging code doesn't like it because we are
> violating typical usage - so the patch is wrong :)
> 
> thanks,
> Tobin.
>