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) >> 6; }
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, 0, "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 = 0; #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) & 1; #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 0; bad_area: do_bad_area(addr, fsr, regs); return 0; }
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)----------------------------------------------------------------------------------4. 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)----5. 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) --------------------------------------------------6. 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(1); 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(0); 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 != 1) 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 != 1) 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(0); 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(1); 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(0); 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 1; 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 0; } void print_modules(void) { struct module *mod; char buf[8]; 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[0]) pr_cont(" [last unloaded: %s]", last_unloaded_module); pr_cont("\n"); } void __show_regs(struct pt_regs *regs) { unsigned long flags; char buf[64]; 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[0] = flags & PSR_N_BIT ? 'N' : 'n'; buf[1] = flags & PSR_Z_BIT ? 'Z' : 'z'; buf[2] = flags & PSR_C_BIT ? 'C' : 'c'; buf[3] = flags & PSR_V_BIT ? 'V' : 'v'; buf[4] = '\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] = '\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 & ~31; first < top; first += 32) { unsigned long p; char str[sizeof(" 12345678") * 8 + 1]; memset(str, ' ', sizeof(str)); str[sizeof(str) - 1] = '\0'; for (p = first, i = 0; i < 8 && p < top; i++, p += 4) { if (p >= bottom && p < top) { unsigned long val; if (__get_user(val, (unsigned long *)p) == 0) sprintf(str + i * 9, " %08lx", val); else sprintf(str + i * 9, " ????????"); } } 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 ? 4 : 8; mm_segment_t fs; char str[sizeof("00000000 ") * 5 + 2 + 1], *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 = -4; i < 1 + !!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 ? "(%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[1024]; va_list args; long i, i_next = 0; int state = 0; /* * 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(1); 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 <= 1) 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, 0, buf);----------------------执行panic_notifier_list链表上的notifier。 bust_spinlocks(0); if (!panic_blink) panic_blink = no_blink; if (panic_timeout > 0) {-------------------------------------------------------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 = 0; i < panic_timeout * 1000; i += PANIC_TIMER_STEP) { touch_nmi_watchdog(); if (i >= i_next) { i += panic_blink(state ^= 1); i_next = i + 3600 / PANIC_BLINK_SPD; } mdelay(PANIC_TIMER_STEP); } } if (panic_timeout != 0) { /* * 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
