linux-kernel - Re: [PATCH 1/7] mm: allocate mm_cpumask dynamically based on nr_cpu

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Message-ID: <201806210526.ySVyrZ56%fengguang.wu@intel.com>
Date:   Thu, 21 Jun 2018 05:32:58 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Rik van Riel <riel@...riel.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        86@...r.kernel.org, luto@...nel.org, mingo@...nel.org,
        tglx@...utronix.de, dave.hansen@...ux.intel.com, efault@....de,
        songliubraving@...com, kernel-team@...com,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 1/7] mm: allocate mm_cpumask dynamically based on
 nr_cpu_ids

Hi Rik,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on v4.17]
[also build test ERROR on next-20180620]
[cannot apply to tip/x86/core linus/master mmotm/master v4.18-rc1]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Rik-van-Riel/x86-tlb-mm-make-lazy-TLB-mode-even-lazier/20180621-045620
config: x86_64-randconfig-x016-201824 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

Note: the linux-review/Rik-van-Riel/x86-tlb-mm-make-lazy-TLB-mode-even-lazier/20180621-045620 HEAD 7f2e7d915758c367dd0515efc17af977592fa141 builds fine.
      It only hurts bisectibility.

All errors (new ones prefixed by >>):

>> mm/init-mm.c:38:1: error: Only string constants are supported as initializers for randomized structures with flexible arrays
    };
    ^

vim +38 mm/init-mm.c

bb1f17b0 Alexey Dobriyan   2009-06-16  17  
c59b389d Rik van Riel      2018-06-20  18  /*
c59b389d Rik van Riel      2018-06-20  19   * For dynamically allocated mm_structs, there is a dynamically sized cpumask
c59b389d Rik van Riel      2018-06-20  20   * at the end of the structure, the size of which depends on nr_cpu_ids. That
c59b389d Rik van Riel      2018-06-20  21   * way we allocate only as much memory for mm_cpumask() as needed for the
c59b389d Rik van Riel      2018-06-20  22   * hundreds, or thousands of processes that a system typically runs.
c59b389d Rik van Riel      2018-06-20  23   *
c59b389d Rik van Riel      2018-06-20  24   * Since there is only one init_mm in the entire system, keep it simple
c59b389d Rik van Riel      2018-06-20  25   * and size this cpu_bitmask to NR_CPUS.
c59b389d Rik van Riel      2018-06-20  26   */
bb1f17b0 Alexey Dobriyan   2009-06-16  27  struct mm_struct init_mm = {
bb1f17b0 Alexey Dobriyan   2009-06-16  28  	.mm_rb		= RB_ROOT,
bb1f17b0 Alexey Dobriyan   2009-06-16  29  	.pgd		= swapper_pg_dir,
bb1f17b0 Alexey Dobriyan   2009-06-16  30  	.mm_users	= ATOMIC_INIT(2),
bb1f17b0 Alexey Dobriyan   2009-06-16  31  	.mm_count	= ATOMIC_INIT(1),
bb1f17b0 Alexey Dobriyan   2009-06-16  32  	.mmap_sem	= __RWSEM_INITIALIZER(init_mm.mmap_sem),
bb1f17b0 Alexey Dobriyan   2009-06-16  33  	.page_table_lock =  __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
bb1f17b0 Alexey Dobriyan   2009-06-16  34  	.mmlist		= LIST_HEAD_INIT(init_mm.mmlist),
bfedb589 Eric W. Biederman 2016-10-13  35  	.user_ns	= &init_user_ns,
c59b389d Rik van Riel      2018-06-20  36  	.cpu_bitmap	= { [BITS_TO_LONGS(NR_CPUS)] = 0},
a1b200e2 Heiko Carstens    2010-08-09  37  	INIT_MM_CONTEXT(init_mm)
bb1f17b0 Alexey Dobriyan   2009-06-16 @38  };

:::::: The code at line 38 was first introduced by commit
:::::: bb1f17b0372de93758653ca3454bc0df18dc2e5c mm: consolidate init_mm definition

:::::: TO: Alexey Dobriyan <adobriyan@...il.com>
:::::: CC: Linus Torvalds <torvalds@...ux-foundation.org>

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