Linux内存管理 (23)一个内存Oops解析

专题：Linux内存管理专题

关键词：DataAbort、fsr、pte、backtrace、stack。

 

在内存相关实际应用中，内存异常访问是一种常见的问题。

本文结合异常T32栈回溯、Oops打印以及代码，分析打印log，加深对Oops的理解，有助于快速定位问题解决问题。

1. 不同类型异常处理

当内存访问异常时，触发__dabt_svc异常向量处理，进入do_DataAbort进行处理。

从_dabt_svc到do_DataAbort流程，可以参考do_DataAbort。

从do_DataAbort开始，fsr_fs()根据fsr找到fsr_info中的处理函数。

asmlinkage void __exception
do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
    const struct fsr_info *inf = fsr_info + fsr_fs(fsr);
    struct siginfo info;

    if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))------------------这里根据fsr从fsr_info中找打对应的操作函数。
        return;
...
}

static inline int fsr_fs(unsigned int fsr)
{
    return (fsr & FSR_FS3_0) | (fsr & FSR_FS4) >> ;
}

fsr_info列出了全部的错误类型，主要包括四种类型：section translation fault、page translation fault、section permission fault、page permission fault。

2. Section Translation Fault

2.1 Section Translation Fault栈信息

下面是一个Section Translation Fault错误实例的T32栈：

fsr=0x805，即100000000101，所以经过fsr_fs()处理返回值为101。

所以inf->fn即为do_translation_fault。

static struct fsr_info fsr_info[] = {
...
    { do_translation_fault,    SIGSEGV, SEGV_MAPERR,    "section translation fault"       },
    { do_bad,        SIGBUS,     ,        "external abort on linefetch"       },
    { do_page_fault,    SIGSEGV, SEGV_MAPERR,    "page translation fault"       },
...
}

可以看出此错误的栈回溯，do_DataAbort根据异常地址、fsr、pt_regs，来判断异常发生在内核还是用户空间，当前状态是用户模式还是非用户模式，fsr用于确定错误处理函数。

__dabt_svc
  ->do_DataAbort
    ->do_translation_fault
      ->do_bad_area
        ->__do_kernel_fault
          ->die

2.2 入口函数do_translation_fault

Section Translation Fault类型的错误处理函数是do_translation_fault。

static int __kprobes
do_translation_fault(unsigned long addr, unsigned int fsr,
             struct pt_regs *regs)
{
    unsigned int index;
    pgd_t *pgd, *pgd_k;
    pud_t *pud, *pud_k;
    pmd_t *pmd, *pmd_k;

    if (addr < TASK_SIZE)-------------------------------------TASK_SIZE是用户空间地址的顶部，所以do_page_fault是用户空间处理函数。
        return do_page_fault(addr, fsr, regs);

    if (user_mode(regs))--------------------------------------至此的地址都是内核空间，如果regs显式为用户空间。说明两者冲突，进入bad_area。
        goto bad_area;

    index = pgd_index(addr);

    pgd = cpu_get_pgd() + index;
    pgd_k = init_mm.pgd + index;

    if (pgd_none(*pgd_k))-------------------------------------pgd_none()返回0，所以不会进入bad_area。
        goto bad_area;
    if (!pgd_present(*pgd))
        set_pgd(pgd, *pgd_k);

    pud = pud_offset(pgd, addr);
    pud_k = pud_offset(pgd_k, addr);

    if (pud_none(*pud_k))-------------------------------------pud_none()同样返回0，不会进入bad_area。
        goto bad_area;
    if (!pud_present(*pud))
        set_pud(pud, *pud_k);

    pmd = pmd_offset(pud, addr);
    pmd_k = pmd_offset(pud_k, addr);

#ifdef CONFIG_ARM_LPAE
    /*
     * Only one hardware entry per PMD with LPAE.
     */
    index = ;
#else
    /*
     * On ARM one Linux PGD entry contains two hardware entries (see page
     * tables layout in pgtable.h). We normally guarantee that we always
     * fill both L1 entries. But create_mapping() doesn't follow the rule.
     * It can create inidividual L1 entries, so here we have to call
     * pmd_none() check for the entry really corresponded to address, not
     * for the first of pair.
     */
    index = (addr >> SECTION_SHIFT) & ;
#endif
    if (pmd_none(pmd_k[index]))------------------------------如果此时pmd_k[index]为0，则为异常进入bad_area。
        goto bad_area;

    copy_pmd(pmd, pmd_k);
    return ;

bad_area:
do_bad_area(addr, fsr, regs);
    return ;
}

如果确实是异常，进入do_bad_area()进行处理。分为user_mode和非user_mode两种模式分别进行处理。

user_mode处理较简单，发送SIGSEGV信号即可。

void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
    struct task_struct *tsk = current;
    struct mm_struct *mm = tsk->active_mm;

    /*
     * If we are in kernel mode at this point, we
     * have no context to handle this fault with.
     */
    if (user_mode(regs))
        __do_user_fault(tsk, addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
    else
__do_kernel_fault(mm, addr, fsr, regs);
}

其它模式交给__do_kernel_fault进行处理，调用流程和打印结果如下。

2.3 内核空间Section Translation Fault处理

__do_kernel_fault的主要工作是打印pte、pt_regs、栈等信息，帮助发现问题根源，核心函数是__die。

__do_kernel_fault  ->show_pte----------------------------------------------------1
  ->die
    ->__die
      ->print_modules-------------------------------------------2
      ->__show_regs---------------------------------------------3
      ->dump_mem------------------------------------------------4
      ->dump_backtrace------------------------------------------5
      ->dump_instr----------------------------------------------6
    ->panic-----------------------------------------------------7

下面是打印结果，结合代码和打印信息进行分析如下：

<1>[153780.197326] Unable to handle kernel paging request at virtual address d8660000------0. 错误概述

<1>[153780.204406] pgd = c287c000---------------------------------------------------------------------------1. show_pte，当前pgd地址0xc287c000

<1>[153780.207183] [d8660000] *pgd=00000000-----------------------------------------------------------异常地址0xd8660000和其对应的pgd表项内容0x00000000，问题就出在这里。

<0>[153780.210845] Internal error: Oops: 805 [#1] ARM--------------------------------- ----------------0. die

<4>[153780.215362] Modules linked in:------------------------------------------------------------------------2. print_modules

<4>[153780.218475] CPU: 0    Not tainted  (3.4.110 #2)---------------------------------------------------3. __show_regs

<4>[153780.223083] PC is at __mutex_lock_slowpath+0x34/0xb8

<4>[153780.228118] LR is at dpm_prepare+0x58/0x1d0

<4>[153780.232360] pc : [<c04ad5bc>]    lr : [<c01a27a8>]    psr: 80000013

<4>[153780.232391] sp : c2d01e58  ip : 00000000  fp : c2cc6800

<4>[153780.243988] r10: c0690bfc  r9 : c0690c04  r8 : c3682c68

<4>[153780.249298] r7 : c3682c64  r6 : c2c2c000  r5 : c3682c30  r4 : c3682c64

<4>[153780.255889] r3 : d8660000  r2 : c2d01e5c  r1 : 00000000  r0 : c3682c64

<4>[153780.262512] Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel---Nzcv大写表示置位；IRQ/FIQ都打开；处于SVC_32模式；架构是ARM；处于内核中。

<4>[153780.269866] Control: 10c5383d  Table: 2287c059  DAC: 00000015

<4>[153780.275695] -----------------------------------------------------------------------------------------------------下面大段show_extra_register_data打印pt_regs前后128字节十六进制值

<4>[153780.275695] PC: 0xc04ad53c:

<4>[153780.280120] d53c  1afffffb e3510001 0afffff6 eaffffb9 e92d4008 e5b03004 e1530000 0a000001

<4>[153780.288360] d55c  e5930008 ebee2a57 e8bd8008 e3a03001 e1901f9f e180cf93 e33c0000 1afffffb

<4>[153780.296630] d57c  e3510000 012fff1e eafffff0 e92d41f0 e24dd010 e1a0200d e1a04000 e3c23d7f

<4>[153780.304870] d59c  e3c3303f e593600c e5903008 e28d2004 e2808004 e5802008 e58d8004 e58d3008

<4>[153780.313110] d5bc  e5832000 e58d600c e3e05000 e1903f9f e1802f95 e3320000 1afffffb e3530001

<4>[153780.321350] d5dc  0a00000e e1903f9f e1802f95 e3320000 1afffffb e3530001 0a000008 e3a07002

<4>[153780.329620] d5fc  e5867000 eb000433 e1943f9f e1842f95 e3320000 1afffffb e3530001 1afffff7

<4>[153780.337860] d61c  e99d000c e5823004 e5832000 e5943004 e1580003 03a03000 05843000 e28dd010

<4>[153780.346099]

<4>[153780.346130] LR: 0xc01a2728:

<4>[153780.350524] 2728  e5812090 e587308c eaffffd2 c0690bd8 c06e4e9c c067f0e8 c0690bf4 c01a1d0c

<4>[153780.358795] 2748  c059e114 c06e4ea0 e92d4ff8 e59f81b8 e1a00008 e288a024 eb0c2bb6 e288902c

<4>[153780.367034] 2768  ea000003 e37b000b 1a00005e e1a00005 ebffda19 e5984024 e154000a 0a000054

<4>[153780.375274] 2788  e2445054 e2447020 e1a00005 ebffda09 e59f0174 eb0c2b71 e1a00007 eb0c2ba5

<4>[153780.383544] 27a8  e5543004 e2131001 0a000002 e5941014 e2911000 13a01001 e59420a4 e5d43018

<4>[153780.391784] 27c8  e3520000 e7c03011 e5c43018 0a000038 e5926000 e3560000 0a000027 e1a00005

<4>[153780.400024] 27e8  e12fff36 e1a0b000 e1a01006 e1a0200b e59f0118 ebfff983 e1a00007 eb0c2b57

<4>[153780.408264] 2808  e59f0104 eb0c2b8b e35b0000 1affffd4 e5943000 e5542004 e1540003 e3822004

<4>[153780.416534]

<4>[153780.416534] SP: 0xc2d01dd8:

<4>[153780.420959] 1dd8  c06be940 c067ccb8 0000000a c2d01df8 c00190b0 c00193f4 60000013 0000000a

<4>[153780.429199] 1df8  c04ad5bc 80000013 ffffffff c2d01e44 c3682c68 c0008cd8 c3682c64 00000000

<4>[153780.437438] 1e18  c2d01e5c d8660000 c3682c64 c3682c30 c2c2c000 c3682c64 c3682c68 c0690c04

<4>[153780.445709] 1e38  c0690bfc c2cc6800 00000000 c2d01e58 c01a27a8 c04ad5bc 80000013 ffffffff

<4>[153780.453948] 1e58  00000010 c3682c68 d8660000 c07b2f78 c3682c84 c3682c30 00000000 c3682c64

<4>[153780.462188] 1e78  c0690bd8 c01a27a8 00000000 00000002 00000000 00000003 000d6508 00000000

<4>[153780.470458] 1e98  c06d01c8 c2d00000 c2cc6800 c01a292c c06d0748 c004092c 00000003 c04b4340

<4>[153780.478698] 1eb8  00000000 000d6508 00000000 c0040d94 c06d0834 00000000 c06e6f4c c06e8f68

<4>[153780.486938]

<4>[153780.486938] FP: 0xc2cc6780:

<4>[153780.491363] 6780  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

<4>[153780.499633] 67a0  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

<4>[153780.507873] 67c0  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

<4>[153780.516113] 67e0  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

<4>[153780.524353] 6800  c06d01c8 c2cba600 00000000 ffffffff 00000001 00000000 00000000 00000000

<4>[153780.532623] 6820  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

<4>[153780.540863] 6840  00000000 00000000 00000000 00000001 00000001 c2cc6854 c2cc6854 c2cc6800

<4>[153780.549102] 6860  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

<4>[153780.557373]

<4>[153780.557373] R0: 0xc3682be4:

<4>[153780.561798] 2be4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.570037] 2c04  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 00000000 00000000

<4>[153780.578277] 2c24  00000000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.586547] 2c44  d8660000 d8660000 d8660000 d8660000 d8660001 d8660000 d8660000 d8660000

<4>[153780.594787] 2c64  ffffffff d8660000 c2d01e5c d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.603027] 2c84  d8660000 c0690bfc d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.611297] 2ca4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.619537] 2cc4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.627777]

<4>[153780.627777] R2: 0xc2d01ddc:

<4>[153780.632202] 1ddc  c067ccb8 0000000a c2d01df8 c00190b0 c00193f4 60000013 0000000a c04ad5bc

<4>[153780.640472] 1dfc  80000013 ffffffff c2d01e44 c3682c68 c0008cd8 c3682c64 00000000 c2d01e5c

<4>[153780.648712] 1e1c  d8660000 c3682c64 c3682c30 c2c2c000 c3682c64 c3682c68 c0690c04 c0690bfc

<4>[153780.656951] 1e3c  c2cc6800 00000000 c2d01e58 c01a27a8 c04ad5bc 80000013 ffffffff 00000010

<4>[153780.665191] 1e5c  c3682c68 d8660000 c07b2f78 c3682c84 c3682c30 00000000 c3682c64 c0690bd8

<4>[153780.673461] 1e7c  c01a27a8 00000000 00000002 00000000 00000003 000d6508 00000000 c06d01c8

<4>[153780.681701] 1e9c  c2d00000 c2cc6800 c01a292c c06d0748 c004092c 00000003 c04b4340 00000000

<4>[153780.689941] 1ebc  000d6508 00000000 c0040d94 c06d0834 00000000 c06e6f4c c06e8f68 c06e6f4c

<4>[153780.698211]

<4>[153780.698211] R3: 0xd865ff80:

<4>[153780.702636] ff80  ******** ******** ******** ******** ******** ******** ******** ********

<4>[153780.710876] ffa0  ******** ******** ******** ******** ******** ******** ******** ********

<4>[153780.719116] ffc0  ******** ******** ******** ******** ******** ******** ******** ********

<4>[153780.727386] ffe0  ******** ******** ******** ******** ******** ******** ******** ********

<4>[153780.735626] 0000  ******** ******** ******** ******** ******** ******** ******** ********

<4>[153780.743865] 0020  ******** ******** ******** ******** ******** ******** ******** ********

<4>[153780.752136] 0040  ******** ******** ******** ******** ******** ******** ******** ********

<4>[153780.760375] 0060  ******** ******** ******** ******** ******** ******** ******** ********

<4>[153780.768615]

<4>[153780.768615] R4: 0xc3682be4:

<4>[153780.773040] 2be4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.781280] 2c04  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 00000000 00000000

<4>[153780.789550] 2c24  00000000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.797790] 2c44  d8660000 d8660000 d8660000 d8660000 d8660001 d8660000 d8660000 d8660000

<4>[153780.806030] 2c64  ffffffff d8660000 c2d01e5c d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.814300] 2c84  d8660000 c0690bfc d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.822540] 2ca4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.830780] 2cc4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.839050]

<4>[153780.839050] R5: 0xc3682bb0:

<4>[153780.843475] 2bb0  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.851715] 2bd0  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.859954] 2bf0  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.868225] 2c10  d8660000 d8660000 d8660000 00000000 00000000 00000000 d8660000 d8660000

<4>[153780.876464] 2c30  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.884704] 2c50  d8660000 d8660001 d8660000 d8660000 d8660000 ffffffff d8660000 c2d01e5c

<4>[153780.892944] 2c70  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 c0690bfc d8660000

<4>[153780.901214] 2c90  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.909454]

<4>[153780.909454] R6: 0xc2c2bf80:

<4>[153780.913879] bf80  f0000188 000181a4 00000000 00000000 00000000 00000000 c04bb340 c06aafbc

<4>[153780.922119] bfa0  c2c2bf00 c2c2b380 00000000 c3708000 00000000 00000000 00000001 00000000

<4>[153780.930389] bfc0  00000000 c2c2bfc4 c2c2bfc4 66756208 666e695f 72a5006f 7ae75aad 5aa55aa5

<4>[153780.938629] bfe0  5aa55ac5 52a75aa0 4a255aa5 5aa45aa5 5aa55aa5 1aa54aa5 08a55ae5 42a552ad

<4>[153780.946868] c000  00000000 c2d00000 00000002 04208040 00000000 00000001 00000064 00000064

<4>[153780.955139] c020  00000064 00000000 c04b4078 00000000 00015ab9 0000bd04 00000001 00000000

<4>[153780.963378] c040  00000000 c2c2c044 c2c2c044 00000001 be05bcc5 00008bdc 02e98615 00000000

<4>[153780.971618] c060  adc99ea7 00000105 01f7d876 00000000 00000000 00000000 00000000 00000000

<4>[153780.979888]

<4>[153780.979888] R7: 0xc3682be4:

<4>[153780.984313] 2be4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153780.992553] 2c04  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 00000000 00000000

<4>[153781.000793] 2c24  00000000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.009063] 2c44  d8660000 d8660000 d8660000 d8660000 d8660001 d8660000 d8660000 d8660000

<4>[153781.017303] 2c64  ffffffff d8660000 c2d01e5c d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.025543] 2c84  d8660000 c0690bfc d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.033782] 2ca4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.042053] 2cc4  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.050292]

<4>[153781.050292] R8: 0xc3682be8:

<4>[153781.054718] 2be8  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.062957] 2c08  d8660000 d8660000 d8660000 d8660000 d8660000 00000000 00000000 00000000

<4>[153781.071228] 2c28  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.079467] 2c48  d8660000 d8660000 d8660000 d8660001 d8660000 d8660000 d8660000 ffffffff

<4>[153781.087707] 2c68  d8660000 c2d01e5c d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.095977] 2c88  c0690bfc d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.104217] 2ca8  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.112457] 2cc8  d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000 d8660000

<4>[153781.120727]

<4>[153781.120727] R9: 0xc0690b84:

<4>[153781.125152] 0b84  c019fcac 00000000 c05b339c 00000124 c019fc00 00000000 c05b33b0 00000124

<4>[153781.133392] 0ba4  c019fb54 00000000 c05b33d0 000001a4 c019f8b0 c019fb00 00000000 c0690bc0

<4>[153781.141632] 0bc4  c0690bc0 00000000 00000001 c0690bd0 c0690bd0 00000001 c0690bdc c0690bdc

<4>[153781.149902] 0be4  c0690be4 c0690be4 c0690bec c0690bec c0690bf4 c0690bf4 c3682c84 c283fb04

<4>[153781.158142] 0c04  c06907c4 c36b4454 c2ae03d4 c3411e44 c0690c14 c0690c14 00000000 c0690c20

<4>[153781.166381] 0c24  c0690c20 00000005 00000100 c0690c30 c0690c30 c01a5354 c05b31c8 00000000

<4>[153781.174621] 0c44  c0690cb8 00000000 00000000 c3413ac0 c01a5b3c 00000000 00000000 c01a5ae4

<4>[153781.182891] 0c64  00000000 00000000 00000000 00000000 00000000 c348bf00 0000003c c05b5d00

<4>[153781.191131]

<4>[153781.191131] R10: 0xc0690b7c:

<4>[153781.195648] 0b7c  c05b3388 00000124 c019fcac 00000000 c05b339c 00000124 c019fc00 00000000

<4>[153781.203887] 0b9c  c05b33b0 00000124 c019fb54 00000000 c05b33d0 000001a4 c019f8b0 c019fb00

<4>[153781.212158] 0bbc  00000000 c0690bc0 c0690bc0 00000000 00000001 c0690bd0 c0690bd0 00000001

<4>[153781.220397] 0bdc  c0690bdc c0690bdc c0690be4 c0690be4 c0690bec c0690bec c0690bf4 c0690bf4

<4>[153781.228637] 0bfc  c3682c84 c283fb04 c06907c4 c36b4454 c2ae03d4 c3411e44 c0690c14 c0690c14

<4>[153781.236877] 0c1c  00000000 c0690c20 c0690c20 00000005 00000100 c0690c30 c0690c30 c01a5354

<4>[153781.245147] 0c3c  c05b31c8 00000000 c0690cb8 00000000 00000000 c3413ac0 c01a5b3c 00000000

<4>[153781.253387] 0c5c  00000000 c01a5ae4 00000000 00000000 00000000 00000000 00000000 c348bf00

<0>[153781.261627] Process suspend (pid: 755, stack limit = 0xc2d00268)--------------线程名是suspend，pid是755，栈的最底部是0xc2d00268，也即sp的指针不能小于此值。

<0>[153781.267730] Stack: (0xc2d01e58 to 0xc2d02000)----------------------------------------------------------------------------------. dump_mem，有前面可知栈的底部，8K对齐则是栈的顶部。

<0>[153781.272155] 1e40:                                                       00000010 c3682c68--------------------------------------------------从栈的底部开始dump，直到栈的顶部。

<0>[153781.280395] 1e60: d8660000 c07b2f78 c3682c84 c3682c30 00000000 c3682c64 c0690bd8 c01a27a8

<0>[153781.288635] 1e80: 00000000 00000002 00000000 00000003 000d6508 00000000 c06d01c8 c2d00000

<0>[153781.296905] 1ea0: c2cc6800 c01a292c c06d0748 c004092c 00000003 c04b4340 00000000 000d6508

<0>[153781.305145] 1ec0: 00000000 c0040d94 c06d0834 00000000 c06e6f4c c06e8f68 c06e6f4c c0690c1c

<0>[153781.313385] 1ee0: 000d6508 c06e8f68 c06e6f4c c0690c1c 000d6508 c01a5390 c067eaf0 00000000

<0>[153781.321655] 1f00: c2d01f9c c04ae1e0 00000000 c2c2c000 c067eaf0 386f67b6 1432efb3 00000000

<0>[153781.329895] 1f20: c2d01f7c c003a910 895c6980 00000000 7bb36301 00000000 00000000 895c6980

<0>[153781.338134] 1f40: 00000000 c2c2c000 c0690c2c c2cc79c0 00000000 c2cc6800 00000000 c002b7cc

<0>[153781.346405] 1f60: 00000064 c2c2c000 c067eaf0 c2cc79c0 c2cc79d4 c2d00000 c2cc79d4 00000001

<0>[153781.354644] 1f80: c06d01c8 00000002 c2cc6800 c002ba10 c06d01c4 c2cc79c0 c2cba600 c002bb28

<0>[153781.362884] 1fa0: c002ba20 c06d01c4 00000000 c341fefc c2cba600 c002ba20 00000013 00000000

<0>[153781.371124] 1fc0: 00000000 00000000 00000000 c0030144 00000000 00000000 c2cba600 00000000

<0>[153781.379394] 1fe0: c2d01fe0 c2d01fe0 c341fefc c00300c0 c0009a20 c0009a20 00000000 00000000

<4>[153781.387664] [<c04ad5bc>] (__mutex_lock_slowpath+0x34/0xb8) from [<c01a27a8>] (dpm_prepare+0x58/0x1d0)----. dump_backtrace

<4>[153781.396942] [<c01a27a8>] (dpm_prepare+0x58/0x1d0) from [<c01a292c>] (dpm_suspend_start+0xc/0x60)

<4>[153781.405792] [<c01a292c>] (dpm_suspend_start+0xc/0x60) from [<c004092c>] (suspend_devices_and_enter+0x58/0x258)

<4>[153781.415863] [<c004092c>] (suspend_devices_and_enter+0x58/0x258) from [<c0040d94>] (pm_suspend+0x268/0x2b0)

<4>[153781.425598] [<c0040d94>] (pm_suspend+0x268/0x2b0) from [<c01a5390>] (suspend+0x3c/0xfc)--------------------dump_backtrace_entry负责打印每条信息，从右到左调用关系

<4>[153781.433654] [<c01a5390>] (suspend+0x3c/0xfc) from [<c002b7cc>] (process_one_work+0x138/0x358)

<4>[153781.442260] [<c002b7cc>] (process_one_work+0x138/0x358) from [<c002ba10>] (process_scheduled_works+0x24/0x34)

<4>[153781.452239] [<c002ba10>] (process_scheduled_works+0x24/0x34) from [<c002bb28>] (rescuer_thread+0x108/0x19c)

<4>[153781.462066] [<c002bb28>] (rescuer_thread+0x108/0x19c) from [<c0030144>] (kthread+0x84/0x90)

<4>[153781.470489] [<c0030144>] (kthread+0x84/0x90) from [<c0009a20>] (kernel_thread_exit+0x0/0x8)

<0>[153781.478881] Code: e2808004 e5802008 e58d8004 e58d3008 (e5832000) --------------------------------------------------. dump_instr

<4>[153781.485168] ---[ end trace 352bcf684b277880 ]---------------------------------------------------------------------------------------oops_exit打印信息

<0>[153781.489746] Kernel panic - not syncing: Fatal exception---------------------------------------------------------------------------7. panic，

__do_kernel_fault主要打印pte页表内容，然后将工作交给die进行处理。

show_pte对pgd、pud、pmd、pte各项进行了检查。

/*
 * Oops.  The kernel tried to access some page that wasn't present.
 */
static void
__do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
          struct pt_regs *regs)
{
    /*
     * Are we prepared to handle this kernel fault?
     */
    if (fixup_exception(regs))
        return;

    /*
     * No handler, we'll have to terminate things with extreme prejudice.
     */
    bust_spinlocks();
    pr_alert("Unable to handle kernel %s at virtual address %08lx\n",
         (addr < PAGE_SIZE) ? "NULL pointer dereference" :
         "paging request", addr);-------------------------------------------用户空间地址显示"NULL pointer dereference"，内核空间地址显示"paging request"。

    show_pte(mm, addr);-----------------------------------------------------打印页表项内容
die("Oops", regs, fsr);-------------------------------------------------Oops die打印，包括modules、pt_regs、stack、backtrace、mem等信息。
    bust_spinlocks();
    do_exit(SIGKILL);
}

/*
 * This is useful to dump out the page tables associated with
 * 'addr' in mm 'mm'.
 */
void show_pte(struct mm_struct *mm, unsigned long addr)
{
    pgd_t *pgd;

    if (!mm)----------------------------------------------------------------如果当前mm为NULL，表示当前进程为内核线程，mm对应init_mm。
        mm = &init_mm;

    pr_alert("pgd = %p\n", mm->pgd);----------------------------------------打印pgd地址
    pgd = pgd_offset(mm, addr);
    pr_alert("[%08lx] *pgd=%08llx",
            addr, (long long)pgd_val(*pgd));--------------------------------打印问题地址和其地址对应的pgd值，注意这里的pgd已经根据地址进行了偏移。

    do {
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

        if (pgd_none(*pgd))
            break;

        if (pgd_bad(*pgd)) {
            pr_cont("(bad)");
            break;
        }

        pud = pud_offset(pgd, addr);
        if (PTRS_PER_PUD != )
            pr_cont(", *pud=%08llx", (long long)pud_val(*pud));

        if (pud_none(*pud))
            break;

        if (pud_bad(*pud)) {
            pr_cont("(bad)");
            break;
        }
---------------------------------------------------------------------对于Linux二级页表映射，上面的判断都可以跳过。
        pmd = pmd_offset(pud, addr);
        if (PTRS_PER_PMD != )
            pr_cont(", *pmd=%08llx", (long long)pmd_val(*pmd));

        if (pmd_none(*pmd))------------------------------------------对于Linux二级页表映射，pmd=pud=pgd，所以*pmd=*pgd。因为实例中*pgd=0x0000，所以此处break。
            break;

        if (pmd_bad(*pmd)) {-----------------------------------------pmd值第2bit必须清零，#define pmd_bad(pmd) (pmd_val(pmd) & 2)
            pr_cont("(bad)");
            break;
        }

        /* We must not map this if we have highmem enabled */
        if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
            break;

        pte = pte_offset_map(pmd, addr);
        pr_cont(", *pte=%08llx", (long long)pte_val(*pte));
#ifndef CONFIG_ARM_LPAE
        pr_cont(", *ppte=%08llx",
               (long long)pte_val(pte[PTE_HWTABLE_PTRS]));
#endif
        pte_unmap(pte);
    } while();

    pr_cont("\n");
}

die将主要工交给__die()打印信息，然后调用panic()执行halt或重启之类的操作。

void die(const char *str, struct pt_regs *regs, int err)
{
    struct thread_info *thread = current_thread_info();
    int ret;
    enum bug_trap_type bug_type = BUG_TRAP_TYPE_NONE;

    oops_enter();

    raw_spin_lock_irq(&die_lock);
    console_verbose();
    bust_spinlocks();
    if (!user_mode(regs))
        bug_type = report_bug(regs->ARM_pc, regs);
    if (bug_type != BUG_TRAP_TYPE_NONE)
        str = "Oops - BUG";
    ret =__die(str, err, thread, regs);

    if (regs && kexec_should_crash(thread->task))
        crash_kexec(regs);---------------------------------------加载并运行调试内核

    bust_spinlocks();
    add_taint(TAINT_DIE);
    raw_spin_unlock_irq(&die_lock);
    oops_exit();------------------------------------------------打印"...end trace..."，表示Oops结束，进入panic阶段。

    if (in_interrupt())
        panic("Fatal exception in interrupt");
    if (panic_on_oops)
panic("Fatal exception");
    if (ret != NOTIFY_STOP)
        do_exit(SIGSEGV);
}

__die输出module信息、ARM寄存器、dump栈、回溯栈等信息。

__show_regs将pt_regs的寄存器打印，并将前后128字节dump出来。

dump_mem将stack二进制dump出来。

dump_backtrace回溯栈并打印出对应符号表信息。

static int __die(const char *str, int err, struct pt_regs *regs)
{
    struct task_struct *tsk = current;
    static int die_counter;
    int ret;

    pr_emerg("Internal error: %s: %x [#%d]" S_PREEMPT S_SMP S_ISA "\n",
             str, err, ++die_counter);

    /* trap and error numbers are mostly meaningless on ARM */
    ret = notify_die(DIE_OOPS, str, regs, err, tsk->thread.trap_no, SIGSEGV);
    if (ret == NOTIFY_STOP)
        return ;

    print_modules();
__show_regs(regs);
    pr_emerg("Process %.*s (pid: %d, stack limit = 0x%p)\n",
         TASK_COMM_LEN, tsk->comm, task_pid_nr(tsk), end_of_stack(tsk));-------end_of_stack是栈的底部。

    if (!user_mode(regs) || in_interrupt()) {
dump_mem(KERN_EMERG, "Stack: ", regs->ARM_sp,
             THREAD_SIZE + (unsigned long)task_stack_page(tsk));---------------dump的范围是当前sp指针到栈的顶部，顶部可以通过task->stack获取，大小固定。sp指向底部。
dump_backtrace(regs, tsk);
dump_instr(KERN_EMERG, regs);
    }

    return ;
}

void print_modules(void)
{
    struct module *mod;
    char buf[];

    printk(KERN_DEFAULT "Modules linked in:");
    /* Most callers should already have preempt disabled, but make sure */
    preempt_disable();
    list_for_each_entry_rcu(mod, &modules, list) {
        if (mod->state == MODULE_STATE_UNFORMED)
            continue;
        pr_cont(" %s%s", mod->name, module_flags(mod, buf));
    }
    preempt_enable();
    if (last_unloaded_module[])
        pr_cont(" [last unloaded: %s]", last_unloaded_module);
    pr_cont("\n");
}

void __show_regs(struct pt_regs *regs)
{
    unsigned long flags;
    char buf[];

    show_regs_print_info(KERN_DEFAULT);

    print_symbol("PC is at %s\n", instruction_pointer(regs));----------PC指针指向的函数以及偏移
    print_symbol("LR is at %s\n", regs->ARM_lr);-----------------------LR指向的函数以及偏移
    printk("pc : [<%08lx>]    lr : [<%08lx>]    psr: %08lx\n"----------打印pt_regs各寄存器值。
           "sp : %08lx  ip : %08lx  fp : %08lx\n",
        regs->ARM_pc, regs->ARM_lr, regs->ARM_cpsr,
        regs->ARM_sp, regs->ARM_ip, regs->ARM_fp);
    printk("r10: %08lx  r9 : %08lx  r8 : %08lx\n",
        regs->ARM_r10, regs->ARM_r9,
        regs->ARM_r8);
    printk("r7 : %08lx  r6 : %08lx  r5 : %08lx  r4 : %08lx\n",
        regs->ARM_r7, regs->ARM_r6,
        regs->ARM_r5, regs->ARM_r4);
    printk("r3 : %08lx  r2 : %08lx  r1 : %08lx  r0 : %08lx\n",
        regs->ARM_r3, regs->ARM_r2,
        regs->ARM_r1, regs->ARM_r0);

    flags = regs->ARM_cpsr;------------------------------------------cpsr的NZCV标志位
    buf[] = flags & PSR_N_BIT ? 'N' : 'n';
    buf[] = flags & PSR_Z_BIT ? 'Z' : 'z';
    buf[] = flags & PSR_C_BIT ? 'C' : 'c';
    buf[] = flags & PSR_V_BIT ? 'V' : 'v';
    buf[] = '\0';

#ifndef CONFIG_CPU_V7M
    printk("Flags: %s  IRQs o%s  FIQs o%s  Mode %s  ISA %s  Segment %s\n",
        buf, interrupts_enabled(regs) ? "n" : "ff",
        fast_interrupts_enabled(regs) ? "n" : "ff",
        processor_modes[processor_mode(regs)],
        isa_modes[isa_mode(regs)],
        get_fs() == get_ds() ? "kernel" : "user");
#else
    printk("xPSR: %08lx\n", regs->ARM_cpsr);
#endif

#ifdef CONFIG_CPU_CP15
    {
        unsigned int ctrl;

        buf[] = '\0';
#ifdef CONFIG_CPU_CP15_MMU
        {
            unsigned int transbase, dac;
            asm("mrc p15, 0, %0, c2, c0\n\t"
                "mrc p15, 0, %1, c3, c0\n"
                : "=r" (transbase), "=r" (dac));
            snprintf(buf, sizeof(buf), "  Table: %08x  DAC: %08x",
                  transbase, dac);
        }
#endif
        asm("mrc p15, 0, %0, c1, c0\n" : "=r" (ctrl));

        printk("Control: %08x%s\n", ctrl, buf);-----------------------输出MMU相关信息
    }
#endif

show_extra_register_data(regs, 128);------------------------------打印pt_regs寄存器地址的前后128字节十六进制

}

/*
 * Dump out the contents of some memory nicely...
 */
static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
             unsigned long top)
{
    unsigned long first;
    mm_segment_t fs;
    int i;

    /*
     * We need to switch to kernel mode so that we can use __get_user
     * to safely read from kernel space.  Note that we now dump the
     * code first, just in case the backtrace kills us.
     */
    fs = get_fs();
    set_fs(KERNEL_DS);

    printk("%s%s(0x%08lx to 0x%08lx)\n", lvl, str, bottom, top);

    for (first = bottom & ~; first < top; first += ) {
        unsigned long p;
        char str[sizeof("") *  + ];

        memset(str, ' ', sizeof(str));
        str[sizeof(str) - ] = '\0';

        for (p = first, i = ; i <  && p < top; i++, p += ) {
            if (p >= bottom && p < top) {
                unsigned long val;
                if (__get_user(val, (unsigned long *)p) == )
                    sprintf(str + i * , " %08lx", val);
                else
                    sprintf(str + i * , " ????????");
            }
        }
        printk("%s%04lx:%s\n", lvl, first & 0xffff, str);
    }

    set_fs(fs);
}

static inline void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
    unwind_backtrace(regs, tsk);
}

void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame)
  {
      #ifdef CONFIG_KALLSYMS
          printk("[<%08lx>] (%pS) from [<%08lx>] (%pS)\n", where, (void *)where, from, (void *)from);
      #else
          printk("Function entered at [<%08lx>] from [<%08lx>]\n", where, from);
      #endif

if (in_exception_text(where))
          dump_mem("", "Exception stack", frame + 4, frame + 4 + sizeof(struct pt_regs));
  }

static void dump_instr(const char *lvl, struct pt_regs *regs)
{
    unsigned long addr = instruction_pointer(regs);
    const int thumb = thumb_mode(regs);
    const int width = thumb ?  : ;
    mm_segment_t fs;
    char str[sizeof("00000000 ") *  +  + ], *p = str;
    int i;

    /*
     * We need to switch to kernel mode so that we can use __get_user
     * to safely read from kernel space.  Note that we now dump the
     * code first, just in case the backtrace kills us.
     */
    fs = get_fs();
    set_fs(KERNEL_DS);

    for (i = -; i <  + !!thumb; i++) {
        unsigned int val, bad;

        if (thumb)
            bad = __get_user(val, &((u16 *)addr)[i]);
        else
            bad = __get_user(val, &((u32 *)addr)[i]);

        if (!bad)
            p += sprintf(p, i ==  ? "(%0*x) " : "%0*x ",
                    width, val);
        else {
            p += sprintf(p, "bad PC value");
            break;
        }
    }
    printk("%sCode: %s\n", lvl, str);

    set_fs(fs);
}

panic()首先打印一条信息"Kernel panic..."，然后执行一些清理操作。

最后执行panic_blink提示，执行重启操作。

void panic(const char *fmt, ...)
{
    static DEFINE_SPINLOCK(panic_lock);
    static char buf[];
    va_list args;
    long i, i_next = ;
    int state = ;

    /*
     * Disable local interrupts. This will prevent panic_smp_self_stop
     * from deadlocking the first cpu that invokes the panic, since
     * there is nothing to prevent an interrupt handler (that runs
     * after the panic_lock is acquired) from invoking panic again.
     */
    local_irq_disable();

    /*
     * It's possible to come here directly from a panic-assertion and
     * not have preempt disabled. Some functions called from here want
     * preempt to be disabled. No point enabling it later though...
     *
     * Only one CPU is allowed to execute the panic code from here. For
     * multiple parallel invocations of panic, all other CPUs either
     * stop themself or will wait until they are stopped by the 1st CPU
     * with smp_send_stop().
     */
    if (!spin_trylock(&panic_lock))
        panic_smp_self_stop();

    console_verbose();
    bust_spinlocks();
    va_start(args, fmt);
    vsnprintf(buf, sizeof(buf), fmt, args);
    va_end(args);
    printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);----------------------panic()的最后最后一条消息
#ifdef CONFIG_DEBUG_BUGVERBOSE
    /*
     * Avoid nested stack-dumping if a panic occurs during oops processing
     */
    if (!test_taint(TAINT_DIE) && oops_in_progress <= )
        dump_stack();
#endif

    /*
     * If we have crashed and we have a crash kernel loaded let it handle
     * everything else.
     * Do we want to call this before we try to display a message?
     */
    crash_kexec(NULL);-------------------------------------------------------------定义CONFIG_KEXEC的情况下，加载调试内核镜像，然后执行。

    /*
     * Note smp_send_stop is the usual smp shutdown function, which
     * unfortunately means it may not be hardened to work in a panic
     * situation.
     */
    smp_send_stop();---------------------------------------------------------------关闭SMP其它核。

    kmsg_dump(KMSG_DUMP_PANIC);----------------------------------------------------执行dump_list上的dumper。

    atomic_notifier_call_chain(&panic_notifier_list, , buf);----------------------执行panic_notifier_list链表上的notifier。

    bust_spinlocks();

    if (!panic_blink)
        panic_blink = no_blink;

    if (panic_timeout > ) {-------------------------------------------------------如果panic_timeout不为0情况下，会在若干秒过后重启。
        /*
         * Delay timeout seconds before rebooting the machine.
         * We can't use the "normal" timers since we just panicked.
         */
        printk(KERN_EMERG "Rebooting in %d seconds..", panic_timeout);

        for (i = ; i < panic_timeout * ; i += PANIC_TIMER_STEP) {
            touch_nmi_watchdog();
            if (i >= i_next) {
                i += panic_blink(state ^= );
                i_next = i +  / PANIC_BLINK_SPD;
            }
            mdelay(PANIC_TIMER_STEP);
        }
    }
    if (panic_timeout != ) {
        /*
         * This will not be a clean reboot, with everything
         * shutting down.  But if there is a chance of
         * rebooting the system it will be rebooted.
         */
        emergency_restart();--------------------------------------------------------执行重启操作。
    }
...
}

3. Section Permission Fault

4. Page Permission Fault