Re: [Kgdb-bugreport] [PATCH] kdb: Avoid using dbg_io_ops until it is initialized

Tim Bird
2011-09-22T17:39:24Z

On 09/21/2011 07:52 PM, Dongdong Deng wrote:
> On Thu, Sep 22, 2011 at 4:19 AM, Tim Bird <tim.bird@am.sony.com> wrote:
>> This fixes a bug with setting a breakpoint during kdb initialization
>> (from kdb_cmds). Any call to kdb_printf() before the initialization
>> of the kgdboc serial console driver (which happens much later during
>> bootup than kdb_init), results in kernel panic due to the use of
>> dbg_io_ops before it is initialized.
>
>
> Did you get the panic for that case?

Yes. See below (without the patch):

[ 0.009552] BUG: unable to handle kernel NULL pointer dereference at 0000001c
[ 0.009999] IP: [<c109112f>] vkdb_printf+0xef/0x690
[ 0.009999] *pde = 00000000
[ 0.009999] Oops: 0000 [#1] SMP
[ 0.009999] Modules linked in:
[ 0.009999]
[ 0.009999] Pid: 0, comm: swapper Not tainted 3.1.0-rc2+ #10 /D865PERL
[ 0.009999] EIP: 0060:[<c109112f>] EFLAGS: 00010002 CPU: 0
[ 0.009999] EIP is at vkdb_printf+0xef/0x690
[ 0.009999] EAX: 00000000 EBX: c18d06c0 ECX: 0000000f EDX: 00000001
[ 0.009999] ESI: 0000000f EDI: c184cd2a EBP: c18adee0 ESP: c18ade70
[ 0.009999] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
[ 0.009999] Process swapper (pid: 0, ti=c18ac000 task=c18b1fa0 task.ti=c18ac000)
[ 0.009999] Stack:
[ 0.009999] c18adef8 c18adeb8 c105ecc2 007a6bc8 00000000 00000202 209db643 00000000
[ 0.009999] c18adeb0 00000000 017f5762 c17f5764 c18adebc c18adf40 00000000 c19db643
[ 0.009999] c18adf08 c1094040 c17f5767 c18adf00 c18adecc c19db720 00000001 00000000
[ 0.009999] Call Trace:
[ 0.009999] [<c105ecc2>] ? sched_clock_local+0xb2/0x190
[ 0.009999] [<c1094040>] ? kdbgetaddrarg+0x80/0x220
[ 0.009999] [<c10916de>] kdb_printf+0xe/0x10
[ 0.009999] [<c1097bc9>] kdb_printbp+0x39/0xc0
[ 0.009999] [<c111cd30>] ? sync_one_sb+0x20/0x20
[ 0.009999] [<c1097e25>] kdb_bp+0x1d5/0x260
[ 0.009999] [<c111cd30>] ? sync_one_sb+0x20/0x20
[ 0.009999] [<c1094ecd>] kdb_parse+0x2ed/0x630
[ 0.009999] [<c1097950>] ? kdb_bt+0x3b0/0x3b0
[ 0.009999] [<c1913208>] ? kdb_initbptab+0x188/0x18e
[ 0.009999] [<c191301b>] kdb_init+0x5d2/0x637
[ 0.009999] [<c19129f1>] dbg_late_init+0x22/0x24
[ 0.009999] [<c18fd7a3>] start_kernel+0x2a8/0x2ea
[ 0.009999] [<c18fd325>] ? kernel_init+0x13a/0x13a
[ 0.009999] [<c18fd0b3>] i386_start_kernel+0xb3/0xbb
[ 0.009999] Code: 00 c6 45 ab 20 c7 45 ac 00 00 00 00 b8 e0 b3 9d c1 e8 76 7a 18 00 8b 15 44 b8 8b c1 85 d2 89 c6 0f 84 1
6 01 00 00 a1 74 65 9d c1 <8b> 78 1c 85 ff 75 19 e9 b3 02 00 00 90 8d 74 26 00 89 d8 89 f1
[ 0.009999] EIP: [<c109112f>] vkdb_printf+0xef/0x690 SS:ESP 0068:c18ade70
[ 0.009999] CR2: 000000000000001c
[ 0.009999] ---[ end trace 4eaa2a86a8e2da22 ]---
[ 0.009999] Kernel panic - not syncing: Attempted to kill the idle task!
[ 0.009999] Pid: 0, comm: swapper Tainted: G D 3.1.0-rc2+ #10
[ 0.009999] Call Trace:
[ 0.009999] [<c160a2f7>] panic+0x57/0x157
[ 0.009999] [<c103ea2b>] do_exit+0x6ab/0x7a0
[ 0.009999] [<c103d2e7>] ? kmsg_dump+0x37/0xc0
[ 0.009999] [<c160a41f>] ? printk+0x28/0x2a
[ 0.009999] [<c160dc45>] oops_end+0x85/0xc0
[ 0.009999] [<c1023ede>] no_context+0xbe/0x150
[ 0.009999] [<c1024000>] __bad_area_nosemaphore+0x90/0x140
[ 0.009999] [<c1041887>] ? irq_exit+0x57/0x90
[ 0.009999] [<c10039d6>] ? do_IRQ+0x46/0xb0
[ 0.009999] [<c160f590>] ? spurious_fault+0xd0/0xd0
[ 0.009999] [<c10240c2>] bad_area_nosemaphore+0x12/0x20
[ 0.009999] [<c160f869>] do_page_fault+0x2d9/0x420
[ 0.009999] [<c121007b>] ? kobject_uevent_env+0x3bb/0x400
[ 0.009999] [<c12164d8>] ? string+0x38/0xc0
[ 0.009999] [<c160f590>] ? spurious_fault+0xd0/0xd0
[ 0.009999] [<c160d1d2>] error_code+0x5a/0x60
[ 0.009999] [<c160f590>] ? spurious_fault+0xd0/0xd0
[ 0.009999] [<c109112f>] ? vkdb_printf+0xef/0x690
[ 0.009999] [<c105ecc2>] ? sched_clock_local+0xb2/0x190
[ 0.009999] [<c1094040>] ? kdbgetaddrarg+0x80/0x220
[ 0.009999] [<c10916de>] kdb_printf+0xe/0x10
[ 0.009999] [<c1097bc9>] kdb_printbp+0x39/0xc0
[ 0.009999] [<c111cd30>] ? sync_one_sb+0x20/0x20
[ 0.009999] [<c1097e25>] kdb_bp+0x1d5/0x260
[ 0.009999] [<c111cd30>] ? sync_one_sb+0x20/0x20
[ 0.009999] [<c1094ecd>] kdb_parse+0x2ed/0x630
[ 0.009999] [<c1097950>] ? kdb_bt+0x3b0/0x3b0
[ 0.009999] [<c1913208>] ? kdb_initbptab+0x188/0x18e
[ 0.009999] [<c191301b>] kdb_init+0x5d2/0x637
[ 0.009999] [<c19129f1>] dbg_late_init+0x22/0x24
[ 0.009999] [<c18fd7a3>] start_kernel+0x2a8/0x2ea
[ 0.009999] [<c18fd325>] ? kernel_init+0x13a/0x13a
[ 0.009999] [<c18fd0b3>] i386_start_kernel+0xb3/0xbb

=============================
Tim Bird
Architecture Group Chair, CE Workgroup of the Linux Foundation
Senior Staff Engineer, Sony Network Entertainment
=============================