lkml.org 
[lkml]   [2018]   [Mar]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v2] Revert "mm/page_alloc: fix memmap_init_zone pageblock alignment"
On Thu, Mar 15, 2018 at 8:36 AM, Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
> On 15 March 2018 at 02:23, Daniel Vacek <neelx@redhat.com> wrote:
>> On Wed, Mar 14, 2018 at 8:29 PM, Ard Biesheuvel
>> <ard.biesheuvel@linaro.org> wrote:
>>> This reverts commit 864b75f9d6b0100bb24fdd9a20d156e7cda9b5ae.
>>>
>>> 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 <neelx@redhat.com>
>>> Cc: Mel Gorman <mgorman@techsingularity.net>
>>> Cc: Michal Hocko <mhocko@suse.com>
>>> Cc: Paul Burton <paul.burton@imgtec.com>
>>> Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
>>> Cc: Vlastimil Babka <vbabka@suse.cz>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: Linus Torvalds <torvalds@linux-foundation.org>
>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@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));
>>
>> Hi, I am on vacation this week and I didn't have a chance to test this
>> yet but I am not sure this is correct. Generic pfn_valid() unlike the
>> arm{,64} arch specific versions returns true for all pfns in a section
>> if there is at least some memory mapped in that section. So I doubt
>> this prevents the crash I was targeting. I believe pfn_valid() does
>> not change a thing here :(
>>
>
> If this is the case, memblock_next_valid_pfn() is broken since it
> skips valid PFNs, and we should be fixing that instead.

How do you define valid pfn? Maybe the generic version of pfn_valid()
should be fixed???

-nX

>> ------------------------
>> include/linux/mmzone.h:
>> pfn_valid(pfn)
>> valid_section(__nr_to_section(pfn_to_section_nr(pfn)))
>> return (section && (section->section_mem_map & SECTION_HAS_MEM_MAP))
>>
>> arch/arm64/mm/init.c:
>> #ifdef CONFIG_HAVE_ARCH_PFN_VALID
>> int pfn_valid(unsigned long pfn)
>> {
>> return memblock_is_map_memory(pfn << PAGE_SHIFT);
>> }
>> EXPORT_SYMBOL(pfn_valid);
>> #endif
>> ------------------------
>>
>> Also I already sent a fix to Andrew yesterday which was reported to
>> fix the loop.
>>
>> Moreover, you also reported this:
>>
>>> Early memory node ranges
>>> node 0: [mem 0x0000000080000000-0x00000000febeffff]
>>> node 0: [mem 0x00000000febf0000-0x00000000fefcffff]
>>> node 0: [mem 0x00000000fefd0000-0x00000000ff43ffff]
>>> node 0: [mem 0x00000000ff440000-0x00000000ff7affff]
>>> node 0: [mem 0x00000000ff7b0000-0x00000000ffffffff]
>>> node 0: [mem 0x0000000880000000-0x0000000fffffffff]
>>> Initmem setup node 0 [mem 0x0000000080000000-0x0000000fffffffff]
>>> pfn:febf0 oldnext:febf0 newnext:fe9ff
>>> pfn:febf0 oldnext:febf0 newnext:fe9ff
>>> pfn:febf0 oldnext:febf0 newnext:fe9ff
>>> etc etc
>>
>> I am wondering how come pfn_valid(0xfebf0) returns false here. Should
>> it be true or do I miss something?
>>
>> --nX

\
 
 \ /
  Last update: 2018-03-15 08:45    [W:0.089 / U:4.952 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site