On 14/03/2018 23:53, Shanker Donthineni wrote:
>
> Hi Ard,
>
> On 03/14/2018 05:25 PM, Jan Glauber wrote:
>> On Wed, Mar 14, 2018 at 07:29:37PM +0000, Ard Biesheuvel wrote:
>>> This reverts commit 864b75f9d6b0100bb24fdd9a20d156e7cda9b5ae.
>>
>> FWIW, the revert fixes the boot hang I'm seeing on ThunderX1.
>>
>> --Jan
>>
>
> Thanks for this patch, it fixes the boot hang on QDF2400 platform.
For the record, this also fixes boot on Amlogic S905X (and for the whole GX
family I presume).
Thanks,
Neil
>
>
>>> Commit 864b75f9d6b0 ("mm/page_alloc: fix memmap_init_zone pageblock
>>> alignment") modified the logic in memmap_init_zone() to initialize
>>> struct pages associated with invalid PFNs, to appease a VM_BUG_ON()
>>> in move_freepages(), which is redundant by its own admission, and
>>> dereferences struct page fields to obtain the zone without checking
>>> whether the struct pages in question are valid to begin with.
>>>
>>> Commit 864b75f9d6b0 only makes it worse, since the rounding it does
>>> may cause pfn assume the same value it had in a prior iteration of
>>> the loop, resulting in an infinite loop and a hang very early in the
>>> boot. Also, since it doesn't perform the same rounding on start_pfn
>>> itself but only on intermediate values following an invalid PFN, we
>>> may still hit the same VM_BUG_ON() as before.
>>>
>>> So instead, let's fix this at the core, and ensure that the BUG
>>> check doesn't dereference struct page fields of invalid pages.
>>>
>>> Fixes: 864b75f9d6b0 ("mm/page_alloc: fix memmap_init_zone pageblock
>>> alignment")
>>> Cc: Daniel Vacek <ne...@redhat.com>
>>> Cc: Mel Gorman <mgor...@techsingularity.net>
>>> Cc: Michal Hocko <mho...@suse.com>
>>> Cc: Paul Burton <paul.bur...@imgtec.com>
>>> Cc: Pavel Tatashin <pasha.tatas...@oracle.com>
>>> Cc: Vlastimil Babka <vba...@suse.cz>
>>> Cc: Andrew Morton <a...@linux-foundation.org>
>>> Cc: Linus Torvalds <torva...@linux-foundation.org>
>>> Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org>
>>> ---
>>> mm/page_alloc.c | 13 +++++--------
>>> 1 file changed, 5 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 3d974cb2a1a1..635d7dd29d7f 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -1910,7 +1910,9 @@ static int move_freepages(struct zone *zone,
>>> * Remove at a later date when no bug reports exist related to
>>> * grouping pages by mobility
>>> */
>>> - VM_BUG_ON(page_zone(start_page) != page_zone(end_page));
>>> + VM_BUG_ON(pfn_valid(page_to_pfn(start_page)) &&
>>> + pfn_valid(page_to_pfn(end_page)) &&
>>> + page_zone(start_page) != page_zone(end_page));
>>> #endif
>>>
>>> if (num_movable)
>>> @@ -5359,14 +5361,9 @@ void __meminit memmap_init_zone(unsigned long size,
>>> int nid, unsigned long zone,
>>> /*
>>> * Skip to the pfn preceding the next valid one (or
>>> * end_pfn), such that we hit a valid pfn (or end_pfn)
>>> - * on our next iteration of the loop. Note that it needs
>>> - * to be pageblock aligned even when the region itself
>>> - * is not. move_freepages_block() can shift ahead of
>>> - * the valid region but still depends on correct page
>>> - * metadata.
>>> + * on our next iteration of the loop.
>>> */
>>> - pfn = (memblock_next_valid_pfn(pfn, end_pfn) &
>>> - ~(pageblock_nr_pages-1)) - 1;
>>> + pfn = memblock_next_valid_pfn(pfn, end_pfn) - 1;
>>> #endif
>>> continue;
>>> }
>>> --
>>> 2.15.1
>>>
>>>
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>>
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