With a kernel configured with ARM64_64K_PAGES && !TRANSPARENT_HUGEPAGE, the following is triggered at early boot:
SMP: Total of 8 processors activated. devtmpfs: initialized Unable to handle kernel NULL pointer dereference at virtual address 00000008 pgd = fffffe0000050000 [00000008] *pgd=00000043fba00003, *pmd=00000043fba00003, *pte=00e0000078010407 Internal error: Oops: 96000006 [#1] SMP Modules linked in: CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.15.0-rc864k+ #44 task: fffffe03bc040000 ti: fffffe03bc080000 task.ti: fffffe03bc080000 PC is at __list_add+0x10/0xd4 LR is at free_one_page+0x270/0x638 ... Call trace: [<fffffe00003ee970>] __list_add+0x10/0xd4 [<fffffe000019c478>] free_one_page+0x26c/0x638 [<fffffe000019c8c8>] __free_pages_ok.part.52+0x84/0xbc [<fffffe000019d5e8>] __free_pages+0x74/0xbc [<fffffe0000c01350>] init_cma_reserved_pageblock+0xe8/0x104 [<fffffe0000c24de0>] cma_init_reserved_areas+0x190/0x1e4 [<fffffe0000090418>] do_one_initcall+0xc4/0x154 [<fffffe0000bf0a50>] kernel_init_freeable+0x204/0x2a8 [<fffffe00007520a0>] kernel_init+0xc/0xd4 This happens because init_cma_reserved_pageblock() calls __free_one_page() with pageblock_order as page order but it is bigger han MAX_ORDER. This in turn causes accesses past zone->free_list[]. Fix the problem by changing init_cma_reserved_pageblock() such that it splits pageblock into individual MAX_ORDER pages if pageblock is bigger than a MAX_ORDER page. In cases where !CONFIG_HUGETLB_PAGE_SIZE_VARIABLE, which is all architectures expect for ia64, powerpc and tile at the moment, the “pageblock_order > MAX_ORDER” condition will be optimised out since both sides of the operator are constants. In cases where pageblock size is variable, the performance degradation should not be significant anyway since init_cma_reserved_pageblock() is called only at boot time at most MAX_CMA_AREAS times which by default is eight. Cc: sta...@vger.kernel.org Signed-off-by: Michal Nazarewicz <min...@mina86.com> Reported-by: Mark Salter <msal...@redhat.com> Tested-by: Christopher Covington <c...@codeaurora.org> --- mm/page_alloc.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) Mark Salter wrote: > I ended up needing this (on top of your patch) to get the system to > boot. Each MAX_ORDER-1 group needs the refcount and migratetype set > so that __free_pages does the right thing. > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 02fb1ed..a7ca6cc 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -799,17 +799,18 @@ void __init init_cma_reserved_pageblock(struct page > *page) > set_page_count(p, 0); > } while (++p, --i); > > - set_page_refcounted(page); > - set_pageblock_migratetype(page, MIGRATE_CMA); > - > - if (pageblock_order > MAX_ORDER) { > - i = pageblock_order - MAX_ORDER; > + if (pageblock_order >= MAX_ORDER) { > + i = pageblock_order - MAX_ORDER + 1; > i = 1 << i; > p = page; > do { > - __free_pages(p, MAX_ORDER); > + set_page_refcounted(p); > + set_pageblock_migratetype(p, MIGRATE_CMA); > + __free_pages(p, MAX_ORDER - 1); > } while (p += MAX_ORDER_NR_PAGES, --i); > } else { > + set_page_refcounted(page); > + set_pageblock_migratetype(page, MIGRATE_CMA); > __free_pages(page, pageblock_order); > } This is kinda embarrassing, dunno how I missed that. But each page actually does not need to have migratetype set, does it? All of those pages are in a single pageblock so a single call suffices. If you track set_pageblock_migratetype down to pfn_to_bitidx there is: return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS; so for pfns inside of a pageblock, they get truncated. Or did I miss yet another thing? diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ee92384..fef9614 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -816,9 +816,21 @@ void __init init_cma_reserved_pageblock(struct page *page) set_page_count(p, 0); } while (++p, --i); - set_page_refcounted(page); set_pageblock_migratetype(page, MIGRATE_CMA); - __free_pages(page, pageblock_order); + + if (pageblock_order >= MAX_ORDER) { + i = pageblock_nr_pages; + p = page; + do { + set_page_refcounted(p); + __free_pages(p, MAX_ORDER - 1); + p += MAX_ORDER_NR_PAGES; + } while (i -= MAX_ORDER_NR_PAGES); + } else { + set_page_refcounted(page); + __free_pages(page, pageblock_order); + } + adjust_managed_page_count(page, pageblock_nr_pages); } #endif -- 2.0.0.526.g5318336 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/