The patch titled Subject: mm: zero remaining unavailable struct pages has been added to the -mm tree. Its filename is mm-zero-remaining-unavailable-struct-pages-re-kernel-panic-in-reading-proc-kpageflags-when-enabling-ram-simulated-pmem.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-zero-remaining-unavailable-struc... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-zero-remaining-unavailable-struc...

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------------------------------------------------------ From: Naoya Horiguchi n-horiguchi@ah.jp.nec.com Subject: mm: zero remaining unavailable struct pages

There is a kernel panic that is triggered when reading /proc/kpageflags on the kernel booted with kernel parameter 'memmap=nn[KMG]!ss[KMG]':

BUG: unable to handle kernel paging request at fffffffffffffffe PGD 9b20e067 P4D 9b20e067 PUD 9b210067 PMD 0 Oops: 0000 [#1] SMP PTI CPU: 2 PID: 1728 Comm: page-types Not tainted 4.17.0-rc6-mm1-v4.17-rc6-180605-0816-00236-g2dfb086ef02c+ #160 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.fc28 04/01/2014 RIP: 0010:stable_page_flags+0x27/0x3c0 Code: 00 00 00 0f 1f 44 00 00 48 85 ff 0f 84 a0 03 00 00 41 54 55 49 89 fc 53 48 8b 57 08 48 8b 2f 48 8d 42 ff 83 e2 01 48 0f 44 c7 <48> 8b 00 f6 c4 01 0f 84 10 03 00 00 31 db 49 8b 54 24 08 4c 89 e7 RSP: 0018:ffffbbd44111fde0 EFLAGS: 00010202 RAX: fffffffffffffffe RBX: 00007fffffffeff9 RCX: 0000000000000000 RDX: 0000000000000001 RSI: 0000000000000202 RDI: ffffed1182fff5c0 RBP: ffffffffffffffff R08: 0000000000000001 R09: 0000000000000001 R10: ffffbbd44111fed8 R11: 0000000000000000 R12: ffffed1182fff5c0 R13: 00000000000bffd7 R14: 0000000002fff5c0 R15: ffffbbd44111ff10 FS: 00007efc4335a500(0000) GS:ffff93a5bfc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: fffffffffffffffe CR3: 00000000b2a58000 CR4: 00000000001406e0 Call Trace: kpageflags_read+0xc7/0x120 proc_reg_read+0x3c/0x60 __vfs_read+0x36/0x170 vfs_read+0x89/0x130 ksys_pread64+0x71/0x90 do_syscall_64+0x5b/0x160 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7efc42e75e23 Code: 09 00 ba 9f 01 00 00 e8 ab 81 f4 ff 66 2e 0f 1f 84 00 00 00 00 00 90 83 3d 29 0a 2d 00 00 75 13 49 89 ca b8 11 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 34 c3 48 83 ec 08 e8 db d3 01 00 48 89 04 24

According to kernel bisection, this problem became visible due to commit f7f99100d8d9 which changes how struct pages are initialized.

Memblock layout affects the pfn ranges covered by node/zone. Consider that we have a VM with 2 NUMA nodes and each node has 4GB memory, and the default (no memmap= given) memblock layout is like below:

MEMBLOCK configuration: memory size = 0x00000001fff75c00 reserved size = 0x000000000300c000 memory.cnt = 0x4 memory[0x0] [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0 memory[0x1] [0x0000000000100000-0x00000000bffd6fff], 0x00000000bfed7000 bytes on node 0 flags: 0x0 memory[0x2] [0x0000000100000000-0x000000013fffffff], 0x0000000040000000 bytes on node 0 flags: 0x0 memory[0x3] [0x0000000140000000-0x000000023fffffff], 0x0000000100000000 bytes on node 1 flags: 0x0 ...

If you give memmap=1G!4G (so it just covers memory[0x2]), the range [0x100000000-0x13fffffff] is gone:

MEMBLOCK configuration: memory size = 0x00000001bff75c00 reserved size = 0x000000000300c000 memory.cnt = 0x3 memory[0x0] [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0 memory[0x1] [0x0000000000100000-0x00000000bffd6fff], 0x00000000bfed7000 bytes on node 0 flags: 0x0 memory[0x2] [0x0000000140000000-0x000000023fffffff], 0x0000000100000000 bytes on node 1 flags: 0x0 ...

This causes shrinking node 0's pfn range because it is calculated by the address range of memblock.memory. So some of struct pages in the gap range are left uninitialized.

We have a function zero_resv_unavail() which does zeroing the struct pages outside memblock.memory, but currently it covers only the reserved unavailable range (i.e. memblock.memory && !memblock.reserved). This patch extends it to cover all unavailable range, which fixes the reported issue.

Link: http://lkml.kernel.org/r/20180613054107.GA5329@hori1.linux.bs1.fc.nec.co.jp Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap") Signed-off-by: Naoya Horiguchi n-horiguchi@ah.jp.nec.com Tested-by: Oscar Salvador osalvador@suse.de Cc: Pavel Tatashin pasha.tatashin@oracle.com Cc: Steven Sistare steven.sistare@oracle.com Cc: Daniel Jordan daniel.m.jordan@oracle.com Cc: "Bob Picco" bob.picco@oracle.com Cc: Matthew Wilcox willy@infradead.org Cc: Michal Hocko mhocko@kernel.org Cc: Huang Ying ying.huang@intel.com Cc: Ingo Molnar mingo@kernel.org Cc: Dan Williams dan.j.williams@intel.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

diff -puN include/linux/memblock.h~mm-zero-remaining-unavailable-struct-pages-re-kernel-panic-in-reading-proc-kpageflags-when-enabling-ram-simulated-pmem include/linux/memblock.h --- a/include/linux/memblock.h~mm-zero-remaining-unavailable-struct-pages-re-kernel-panic-in-reading-proc-kpageflags-when-enabling-ram-simulated-pmem +++ a/include/linux/memblock.h @@ -236,22 +236,6 @@ void __next_mem_pfn_range(int *idx, int for_each_mem_range_rev(i, &memblock.memory, &memblock.reserved, \ nid, flags, p_start, p_end, p_nid)

-/** - * for_each_resv_unavail_range - iterate through reserved and unavailable memory - * @i: u64 used as loop variable - * @flags: pick from blocks based on memory attributes - * @p_start: ptr to phys_addr_t for start address of the range, can be %NULL - * @p_end: ptr to phys_addr_t for end address of the range, can be %NULL - * - * Walks over unavailable but reserved (reserved && !memory) areas of memblock. - * Available as soon as memblock is initialized. - * Note: because this memory does not belong to any physical node, flags and - * nid arguments do not make sense and thus not exported as arguments. - */ -#define for_each_resv_unavail_range(i, p_start, p_end) \ - for_each_mem_range(i, &memblock.reserved, &memblock.memory, \ - NUMA_NO_NODE, MEMBLOCK_NONE, p_start, p_end, NULL) - static inline void memblock_set_region_flags(struct memblock_region *r, unsigned long flags) { diff -puN mm/page_alloc.c~mm-zero-remaining-unavailable-struct-pages-re-kernel-panic-in-reading-proc-kpageflags-when-enabling-ram-simulated-pmem mm/page_alloc.c --- a/mm/page_alloc.c~mm-zero-remaining-unavailable-struct-pages-re-kernel-panic-in-reading-proc-kpageflags-when-enabling-ram-simulated-pmem +++ a/mm/page_alloc.c @@ -6390,25 +6390,40 @@ void __paginginit free_area_init_node(in * struct pages which are reserved in memblock allocator and their fields * may be accessed (for example page_to_pfn() on some configuration accesses * flags). We must explicitly zero those struct pages. + * + * This function also addresses a similar issue where struct pages are left + * uninitialized because the physical address range is not covered by + * memblock.memory or memblock.reserved. That could happen when memblock + * layout is manually configured via memmap=. */ void __paginginit zero_resv_unavail(void) { phys_addr_t start, end; unsigned long pfn; u64 i, pgcnt; + phys_addr_t next = 0;

/* - * Loop through ranges that are reserved, but do not have reported - * physical memory backing. + * Loop through unavailable ranges not covered by memblock.memory. */ pgcnt = 0; - for_each_resv_unavail_range(i, &start, &end) { - for (pfn = PFN_DOWN(start); pfn < PFN_UP(end); pfn++) { - if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) - continue; - mm_zero_struct_page(pfn_to_page(pfn)); - pgcnt++; + for_each_mem_range(i, &memblock.memory, NULL, + NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, NULL) { + if (next < start) { + for (pfn = PFN_DOWN(next); pfn < PFN_UP(start); pfn++) { + if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) + continue; + mm_zero_struct_page(pfn_to_page(pfn)); + pgcnt++; + } } + next = end; + } + for (pfn = PFN_DOWN(next); pfn < max_pfn; pfn++) { + if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) + continue; + mm_zero_struct_page(pfn_to_page(pfn)); + pgcnt++; }

/* @@ -6419,7 +6434,7 @@ void __paginginit zero_resv_unavail(void * this code can be removed. */ if (pgcnt) - pr_info("Reserved but unavailable: %lld pages", pgcnt); + pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt); } #endif /* CONFIG_HAVE_MEMBLOCK */

_

Patches currently in -mm which might be from n-horiguchi@ah.jp.nec.com are

mm-zero-remaining-unavailable-struct-pages-re-kernel-panic-in-reading-proc-kpageflags-when-enabling-ram-simulated-pmem.patch