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Message-ID: <137e4211-266f-bdb3-6830-e101c27c3be4@suse.cz>
Date:   Fri, 15 Oct 2021 10:27:17 +0200
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Subject: Re: [lib/stackdepot] 1cd8ce52c5:
 BUG:unable_to_handle_page_fault_for_address
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To:     Mike Rapoport <rppt@kernel.org>
Cc:     kernel test robot <oliver.sang@intel.com>,
        0day robot <lkp@intel.com>, Dmitry Vyukov <dvyukov@google.com>,
        Marco Elver <elver@google.com>,
        Vijayanand Jitta <vjitta@codeaurora.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Oliver Glitta <glittao@gmail.com>,
        Imran Khan <imran.f.khan@oracle.com>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
        kasan-dev@googlegroups.com
References: <20211014085450.GC18719@xsang-OptiPlex-9020>
 <4d99add1-5cf7-c608-a131-18959b85e5dc@suse.cz> <YWgDkjqtJO4e3DM6@kernel.org>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <YWgDkjqtJO4e3DM6@kernel.org>
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On 10/14/21 12:16, Mike Rapoport wrote:
> On Thu, Oct 14, 2021 at 11:33:03AM +0200, Vlastimil Babka wrote:
>> On 10/14/21 10:54, kernel test robot wrote:
>> 
>> In my local testing of the patch, when stackdepot was initialized through
>> page owner init, it was using kvmalloc() so slab_is_available() was true.
>> Looks like the exact order of slab vs page_owner alloc is non-deterministic,
>> could be arch-dependent or just random ordering of init calls. A wrong order
>> will exploit the apparent fact that slab_is_available() is not a good
>> indicator of using memblock vs page allocator, and we would need a better one.
>> Thoughts?
> 
> The order of slab vs page_owner is deterministic, but it is different for
> FLATMEM and SPARSEMEM. And page_ext_init_flatmem_late() that initializes
> page_ext for FLATMEM is called exactly between buddy and slab setup:

Oh, so it was due to FLATMEM, thanks for figuring that out!

> static void __init mm_init(void)
> {
> 	...
> 
> 	mem_init();
> 	mem_init_print_info();
> 	/* page_owner must be initialized after buddy is ready */
> 	page_ext_init_flatmem_late();
> 	kmem_cache_init();
> 
> 	...
> }
> 
> I've stared for a while at page_ext init and it seems that the
> page_ext_init_flatmem_late() can be simply dropped because there is anyway
> a call to invoke_init_callbacks() in page_ext_init() that is called much
> later in the boot process.

Yeah, but page_ext_init() only does something for SPARSEMEM, and is empty on
FLATMEM. Otherwise it would be duplicating all the work. So I'll just move
page_ext_init_flatmem_late() below kmem_cache_init() in mm_init(). Thanks
again!