On 10/07/2015 11:28 PM, Laura Abbott wrote: > From: Laura Abbott <laura@xxxxxxxxxxxx> > > Srinivas Kandagatla reported bad page messages when trying to > remove the bottom 2MB on an ARM based IFC6410 board > > BUG: Bad page state in process swapper pfn:fffa8 > page:ef7fb500 count:0 mapcount:0 mapping: (null) index:0x0 > flags: 0x96640253(locked|error|dirty|active|arch_1|reclaim|mlocked) > page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > bad because of flags: > flags: 0x200041(locked|active|mlocked) > Modules linked in: > CPU: 0 PID: 0 Comm: swapper Not tainted 3.19.0-rc3-00007-g412f9ba-dirty #816 > Hardware name: Qualcomm (Flattened Device Tree) > [<c0218280>] (unwind_backtrace) from [<c0212be8>] (show_stack+0x20/0x24) > [<c0212be8>] (show_stack) from [<c0af7124>] (dump_stack+0x80/0x9c) > [<c0af7124>] (dump_stack) from [<c0301570>] (bad_page+0xc8/0x128) > [<c0301570>] (bad_page) from [<c03018a8>] (free_pages_prepare+0x168/0x1e0) > [<c03018a8>] (free_pages_prepare) from [<c030369c>] (free_hot_cold_page+0x3c/0x174) > [<c030369c>] (free_hot_cold_page) from [<c0303828>] (__free_pages+0x54/0x58) > [<c0303828>] (__free_pages) from [<c030395c>] (free_highmem_page+0x38/0x88) > [<c030395c>] (free_highmem_page) from [<c0f62d5c>] (mem_init+0x240/0x430) > [<c0f62d5c>] (mem_init) from [<c0f5db3c>] (start_kernel+0x1e4/0x3c8) > [<c0f5db3c>] (start_kernel) from [<80208074>] (0x80208074) > Disabling lock debugging due to kernel taint > > Removing the lower 2MB made the start of the lowmem zone to no longer > be page block aligned. IFC6410 uses CONFIG_FLATMEM where > alloc_node_mem_map allocates memory for the mem_map. alloc_node_mem_map > will offset for unaligned nodes with the assumption the pfn/page > translation functions will account for the offset. The functions for > CONFIG_FLATMEM do not offset however, resulting in overrunning > the memmap array. Just use the allocated memmap without any offset > when running with CONFIG_FLATMEM to avoid the overrun. > > Signed-off-by: Laura Abbott <laura@xxxxxxxxxxxx> > Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx> > Reported-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx> > Tested-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > Tested-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxxxxxx> > > > --- > I was reminded at Linaro Connect that I never followed up on this patch. > v3 (http://marc.info/?l=linux-mm&m=142629173021316&w=2) > was dropped due to crashing (https://lkml.org/lkml/2015/3/20/546) > The fundamentals of the patch were fine, the VM_BUG_ON I added turned out > to be incorrect. It was supposed to be a sanity check but it didn't > actually hold true in all cases (or even most cases...) Yeah, sorry about the VM_BUG_ON (I think I suggested it originally). It's indeed wrong, I can see it now... the self-referentiality of "page_to_pfn(mem_map)" on FLATMEM makes my head hurt. > v4 just drops > the sanity check. I verified that the offset is working on both ARM, x86, > and i386 QEMU with the config provided by Steven Rostedt. Great, thanks. > Since this was minor diff from the previous patch, I kept all the previous > Acked-by/Tested-by. > --- > mm/page_alloc.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 40e2942..9e5ba5e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4953,6 +4953,8 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat, > > static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) > { > + unsigned long __maybe_unused offset = 0; > + > /* Skip empty nodes */ > if (!pgdat->node_spanned_pages) > return; > @@ -4969,6 +4971,7 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) > * for the buddy allocator to function correctly. > */ > start = pgdat->node_start_pfn & ~(MAX_ORDER_NR_PAGES - 1); > + offset = pgdat->node_start_pfn - start; > end = pgdat_end_pfn(pgdat); > end = ALIGN(end, MAX_ORDER_NR_PAGES); > size = (end - start) * sizeof(struct page); > @@ -4976,7 +4979,7 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) > if (!map) > map = memblock_virt_alloc_node_nopanic(size, > pgdat->node_id); > - pgdat->node_mem_map = map + (pgdat->node_start_pfn - start); > + pgdat->node_mem_map = map + offset; > } > #ifndef CONFIG_NEED_MULTIPLE_NODES > /* > @@ -4984,9 +4987,9 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) > */ > if (pgdat == NODE_DATA(0)) { > mem_map = NODE_DATA(0)->node_mem_map; > -#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP > +#if defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) || defined(CONFIG_FLATMEM) > if (page_to_pfn(mem_map) != pgdat->node_start_pfn) > - mem_map -= (pgdat->node_start_pfn - ARCH_PFN_OFFSET); > + mem_map -= offset; > #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */ > } > #endif > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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