Messages in this thread | | | From | Daniel Vacek <> | Date | Thu, 15 Mar 2018 08:44:31 +0100 | Subject | Re: [PATCH v2] Revert "mm/page_alloc: fix memmap_init_zone pageblock alignment" |
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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
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