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    SubjectRe: [PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y
    On Fri, Dec 22, 2017 at 09:45:08AM +0100, Greg Kroah-Hartman wrote:
    > 4.14-stable review patch. If anyone has any objections, please let me know.
    >
    > ------------------
    >
    > From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    >
    > commit 83e3c48729d9ebb7af5a31a504f3fd6aff0348c4 upstream.
    >
    > Size of the mem_section[] array depends on the size of the physical address space.
    >
    > In preparation for boot-time switching between paging modes on x86-64
    > we need to make the allocation of mem_section[] dynamic, because otherwise
    > we waste a lot of RAM: with CONFIG_NODE_SHIFT=10, mem_section[] size is 32kB
    > for 4-level paging and 2MB for 5-level paging mode.
    >
    > The patch allocates the array on the first call to sparse_memory_present_with_active_regions().
    >
    > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Andy Lutomirski <luto@amacapital.net>
    > Cc: Borislav Petkov <bp@suse.de>
    > Cc: Cyrill Gorcunov <gorcunov@openvz.org>
    > Cc: Linus Torvalds <torvalds@linux-foundation.org>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: linux-mm@kvack.org
    > Link: http://lkml.kernel.org/r/20170929140821.37654-2-kirill.shutemov@linux.intel.com
    > Signed-off-by: Ingo Molnar <mingo@kernel.org>
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    This patch causes a boot failure on arm64.

    Please drop this patch, or pick up the fix in:

    commit 629a359bdb0e0652a8227b4ff3125431995fec6e
    Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Date: Tue Nov 7 11:33:37 2017 +0300

    mm/sparsemem: Fix ARM64 boot crash when CONFIG_SPARSEMEM_EXTREME=y

    See https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1527427.html

    >
    > ---
    > include/linux/mmzone.h | 6 +++++-
    > mm/page_alloc.c | 10 ++++++++++
    > mm/sparse.c | 17 +++++++++++------
    > 3 files changed, 26 insertions(+), 7 deletions(-)
    >
    > --- a/include/linux/mmzone.h
    > +++ b/include/linux/mmzone.h
    > @@ -1152,13 +1152,17 @@ struct mem_section {
    > #define SECTION_ROOT_MASK (SECTIONS_PER_ROOT - 1)
    >
    > #ifdef CONFIG_SPARSEMEM_EXTREME
    > -extern struct mem_section *mem_section[NR_SECTION_ROOTS];
    > +extern struct mem_section **mem_section;
    > #else
    > extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
    > #endif
    >
    > static inline struct mem_section *__nr_to_section(unsigned long nr)
    > {
    > +#ifdef CONFIG_SPARSEMEM_EXTREME
    > + if (!mem_section)
    > + return NULL;
    > +#endif
    > if (!mem_section[SECTION_NR_TO_ROOT(nr)])
    > return NULL;
    > return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
    > --- a/mm/page_alloc.c
    > +++ b/mm/page_alloc.c
    > @@ -5651,6 +5651,16 @@ void __init sparse_memory_present_with_a
    > unsigned long start_pfn, end_pfn;
    > int i, this_nid;
    >
    > +#ifdef CONFIG_SPARSEMEM_EXTREME
    > + if (!mem_section) {
    > + unsigned long size, align;
    > +
    > + size = sizeof(struct mem_section) * NR_SECTION_ROOTS;
    > + align = 1 << (INTERNODE_CACHE_SHIFT);
    > + mem_section = memblock_virt_alloc(size, align);
    > + }
    > +#endif
    > +
    > for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, &this_nid)
    > memory_present(this_nid, start_pfn, end_pfn);
    > }
    > --- a/mm/sparse.c
    > +++ b/mm/sparse.c
    > @@ -23,8 +23,7 @@
    > * 1) mem_section - memory sections, mem_map's for valid memory
    > */
    > #ifdef CONFIG_SPARSEMEM_EXTREME
    > -struct mem_section *mem_section[NR_SECTION_ROOTS]
    > - ____cacheline_internodealigned_in_smp;
    > +struct mem_section **mem_section;
    > #else
    > struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
    > ____cacheline_internodealigned_in_smp;
    > @@ -101,7 +100,7 @@ static inline int sparse_index_init(unsi
    > int __section_nr(struct mem_section* ms)
    > {
    > unsigned long root_nr;
    > - struct mem_section* root;
    > + struct mem_section *root = NULL;
    >
    > for (root_nr = 0; root_nr < NR_SECTION_ROOTS; root_nr++) {
    > root = __nr_to_section(root_nr * SECTIONS_PER_ROOT);
    > @@ -112,7 +111,7 @@ int __section_nr(struct mem_section* ms)
    > break;
    > }
    >
    > - VM_BUG_ON(root_nr == NR_SECTION_ROOTS);
    > + VM_BUG_ON(!root);
    >
    > return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
    > }
    > @@ -330,11 +329,17 @@ again:
    > static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
    > {
    > unsigned long usemap_snr, pgdat_snr;
    > - static unsigned long old_usemap_snr = NR_MEM_SECTIONS;
    > - static unsigned long old_pgdat_snr = NR_MEM_SECTIONS;
    > + static unsigned long old_usemap_snr;
    > + static unsigned long old_pgdat_snr;
    > struct pglist_data *pgdat = NODE_DATA(nid);
    > int usemap_nid;
    >
    > + /* First call */
    > + if (!old_usemap_snr) {
    > + old_usemap_snr = NR_MEM_SECTIONS;
    > + old_pgdat_snr = NR_MEM_SECTIONS;
    > + }
    > +
    > usemap_snr = pfn_to_section_nr(__pa(usemap) >> PAGE_SHIFT);
    > pgdat_snr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
    > if (usemap_snr == pgdat_snr)
    >
    >

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