x210启动时遇到Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

目录

引言

错误分析

解决方法

结语

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引言

今天在辅导学生实验时遇到一个奇怪的问题，x210实验箱在启动Linux时频繁报告“Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)”错误，并不断重新启动。刚开始以为是内核的问题，重新烧写了内核，还是存在问题。又重新烧写了文件系统，问题依旧。下面记录一下解决问题的方法。

错误分析

相同启动过程中出现如下错误：

[   20.524222] FIMC0 registered successfully
[   20.528064] FIMC1 registered successfully
[   20.532028] FIMC2 registered successfully
[   20.534801] <6>S5PC1XX TVOUT Driver, (c) 2009 Samsung Electronics
[   20.541474] s5p-tvout s5p-tvout: hpd status is cable removed
[   20.552511] DBUG_PORT must not use AFC!
[   20.555022] VFS: Cannot open root device "(null)" or unknown-block(0,0)
[   20.561471] Please append a correct "root=" boot option; here are the available partitions:
[   20.569815] b300         3866624 mmcblk0 driver: mmcblk
[   20.574968]   b301          264495 mmcblk0p1
[   20.579214]   b302          264495 mmcblk0p2
[   20.583460]   b303          105798 mmcblk0p3
[   20.587706]   b304         3207946 mmcblk0p4
[   20.591953] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[   20.600200] Backtrace:
[   20.602629] [<c0034fb8>] (dump_backtrace+0x0/0x110) from [<c050653c>] (dump_stack+0x18/0x1c)
[   20.611038]  r6:00008000 r5:dfecc000 r4:c06ffb6c r3:00000002
[   20.616653] [<c0506524>] (dump_stack+0x0/0x1c) from [<c05065b8>] (panic+0x78/0xf8)
[   20.624333] [<c0506540>] (panic+0x0/0xf8) from [<c0008f6c>] (mount_block_root+0x25c/0x2ac)
[   20.632441]  r3:00000002 r2:00000001 r1:dfc37f60 r0:c064efba
[   20.638056] [<c0008d10>] (mount_block_root+0x0/0x2ac) from [<c0009010>] (mount_root+0x54/0x68)
[   20.646658] [<c0008fbc>] (mount_root+0x0/0x68) from [<c0009188>] (prepare_namespace+0x164/0x1bc)
[   20.655401]  r5:c00083d4 r4:c073bb40
[   20.658940] [<c0009024>] (prepare_namespace+0x0/0x1bc) from [<c00084fc>] (kernel_init+0x128/0x170)
[   20.667882]  r5:c00083d4 r4:c073b900
[   20.671423] [<c00083d4>] (kernel_init+0x0/0x170) from [<c0058894>] (do_exit+0x0/0x5f0)
[   20.679318]  r4:00000000 r3:00000000
[   20.682858] Rebooting in 5 seconds..
[   25.722580] Restarting Linux version 2.6.35.7 (root@ubuntu) (gcc version 4.4.1 (Sourcery G++ Lite 2009q3-67) ) #2 PREEMPT Mon Jan 14 13:55:33 CST 2019
[   25.722591]
[   25.737831] arch_reset: attempting watchdog reOK

U-Boot 1.3.4-dirty (May 21 2016 - 18:17:00) for x210

根据日志分析，系统在启动时无法挂载根文件系统（rootfs），导致内核恐慌。但是重新烧写了文件系统之后仍然出现问题就让人怀疑U-Boot中关于根文件有关的参数有问题。

解决方法

此问题通常由错误的启动参数或内核驱动缺失导致，优先检查 root= 参数、文件系统驱动及存储设备初始化状态。

打印了该开发板的U-Boot环境参数。

x210 # printenv
bootcmd=movi read kernel 30008000; movi read rootfs 30B00000 300000; bootm 30008000 30B00000
mtdpart=80000 400000 3000000
bootdelay=3
baudrate=115200
ethaddr=00:40:5c:26:0a:5b
ipaddr=192.168.1.88
serverip=192.168.1.102
gatewayip=192.168.0.1
netmask=255.255.0.0

对比了正常启动的开发板的U-Boot参数。

x210 # printenv
mtdpart=80000 400000 3000000
bootdelay=3
baudrate=115200
ethaddr=00:40:5c:26:0a:5b
ipaddr=192.168.1.88
serverip=192.168.1.102
gatewayip=192.168.0.1
netmask=255.255.0.0
bootargs=console=ttySAC2,115200 root=/dev/mmcblk0p2 rw init=/linuxrc rootfstype=ext3
bootcmd=movi read kernel 30008000; bootm 30008000

对比之后发现，出问题的开发板少了bootargs参数，导致在加载文件系统时不知道到哪里去寻找。

在U-Boot中执行以下命令：

setenv bootargs "console=ttySAC2,115200 root=/dev/mmcblk0p2 rw init=/linuxrc rootfstype=ext3"
saveenv

 然后重新启动开发板，一切正常了。

结语

这个问题比较少见，应该是保存环境变量的地方出现了错误，正确恢复环境变量就可以工作了。