Re: [Crash-utility] if it's normal to get into kdb shell when run crash

On 30 December 2015 at 16:34, Liu, Jianbo (James) <James.Liu(a)windriver.com&gt; wrote: Hello James, crash and kgdb are two completely different debuggers to diagnose the kernel panic issues. You can not access or start the crash from the context of kgdb. [**crash utility:**] There are two ways to invoke crash utility[[1]]; 1) Typical postmortem debugging: (after panic) # crash /path/to/vmcore /path/to/vmlinux o Kernel object file and memory image are supplied, respectively. 2) Live memory debugging: # crash o Pre-defined directories are searched for proper vmlinux o Version string matched to the running kernel (/proc/version) **OR** # crash /path/to/vmlinux [**kdb/kgdb:**][[2]] 1) You can put the target system in debug mode using SysRq event (g). # echo g > /proc/sysrq-trigger Eg: # echo g > /proc/sysrq-trigger [ 181.300854] SysRq : DEBUG Entering kdb (current=0xffff8800766ebc60, pid 2347) on processor 1 due to Keyboard Entry [1]kdb> summary sysname Linux release 3.10.84 version #1 SMP Tue Jul 28 19:53:37 IST 2015 machine x86_64 nodename localhost.localdomain domainname (none) ccversion CCVERSION date 2015-12-30 13:51:06 tz_minuteswest 0 uptime 00:03 load avg 0.11 0.11 0.04 MemTotal: 2050340 kB MemFree: 1707332 kB Buffers: 764 kB 1]kdb> dmesg | grep DMI: <7>[ 0.000000] DMI: Red Hat KVM, BIOS 0.5.1 01/01/2007 [1]kdb> bt Stack traceback for pid 2347 0xffff8800766ebc60 2347 624 1 1 R 0xffff8800766ec240 *bash ffff88007bd61e70 0000000000000018 Call Trace: <#DB> <<EOE>> [<ffffffff810dd84c>] ? sysrq_handle_dbg+0x2c/0x50 [<ffffffff8134b312>] ? __handle_sysrq+0xa2/0x170 [<ffffffff8134b80a>] ? write_sysrq_trigger+0x4a/0x50 [<ffffffff811fb61d>] ? proc_reg_write+0x3d/0x80 [<ffffffff811993bd>] ? vfs_write+0xbd/0x1e0 [<ffffffff81199d89>] ? SyS_write+0x49/0xa0 [<ffffffff815a27c7>] ? tracesys+0xdd/0xe2 [1]kdb> rd ax: 0000000000000001 bx: ffffffff818a4560 cx: ffff88007fd0eec0 dx: 0000000000000000 si: 0000000000000000 di: 0000000000000067 bp: ffff88007bd61e70 sp: ffff88007bd61e70 r8: ffffffff81b9069c r9: 0000000000000248 r10: 0000000000000247 r11: 0000000000000003 r12: 0000000000000067 r13: 0000000000000246 r14: 0000000000000007 r15: 0000000000000000 ip: ffffffff810dd7f4 flags: 00000002 cs: 00000010 ss: 00000018 ds: 00000018 es: 00000018 fs: 00000018 gs: 00000018 [1]kdb> go [ 251.553055] systemd-journald[2372]: File /run/log/journal/71b46828837d4b1cb7f04385c86e7626/system.journal corrupted or uncleanly shut down, renaming and replacing. # <<<---{ root user } [Note:] kdb command "go" is used to continue kernel execution. In above case it will take you back to bash shell. 2) You can crash the target system using SysRq event (c): # echo c > /proc/sysrq-trigger Eg: # echo c > /proc/sysrq-trigger [ 28.963227] SysRq : Trigger a crash [ 28.964025] BUG: unable to handle kernel NULL pointer dereference at (null) [ 28.964025] IP: [<ffffffff8134abb6>] sysrq_handle_crash+0x16/0x20 [ 28.964025] Oops: 0002 [#1] SMP Entering kdb (current=0xffff880077275a90, pid 2352) on processor 1 Oops: (null) due to oops @ 0xffffffff8134abb6
dCPU: 1 PID: 2352 Comm: bash Not tainted 3.10.84 #1
dHardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007
dtask: ffff880077275a90 ti: ffff880076494000 task.ti: ffff880076494000
dRIP: 0010:[<ffffffff8134abb6>] [<ffffffff8134abb6>] sysrq_handle_crash+0x16/0x20
dRSP: 0018:ffff880076495e80 EFLAGS: 00010096
dRAX: 000000000000000f RBX: ffffffff8190dbc0 RCX: ffff88007fd0eec0
dRDX: 0000000000000000 RSI: ffff88007fd0d368 RDI: 0000000000000063
dRBP: ffff880076495e80 R08: ffffffff81b9069c R09: 0000000000000245
dR10: 0000000000000244 R11: 0000000000000003 R12: 0000000000000063
dR13: 0000000000000246 R14: 0000000000000007 R15: 0000000000000000
dFS: 00007f53aec0c740(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000
dCS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
dCR2: 0000000000000000 CR3: 00000000764bd000 CR4: 00000000000006e0
dDR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
dDR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
dStack: ffff880076495eb8 ffffffff8134b312 0000000000000002 00007f53aec0a000 ffff880076495f50 0000000000000002 0000000000000000 ffff880076495ed8 ffffffff8134b80a 00007f53aec0a000 ffff88007661c000 ffff880076495ef8
dCall Trace: more> Only 'q' or 'Q' are processed at more prompt, input ignored
d [<ffffffff8134b312>] __handle_sysrq+0xa2/0x170
d [<ffffffff8134b80a>] write_sysrq_trigger+0x4a/0x50
d [<ffffffff811fb61d>] proc_reg_write+0x3d/0x80
d [<ffffffff811993bd>] vfs_write+0xbd/0x1e0
d [<ffffffff81199d89>] SyS_write+0x49/0xa0
d [<ffffffff815a27c7>] tracesys+0xdd/0xe2
dCode: eb 9b 45 01 f4 45 39 65 34 75 e5 4c 89 ef e8 02 f8 ff ff eb db 0f 1f 44 00 00 55 c7 05 20 17 54 00 01 00 00 00 48 89 e5 0f ae f8 <c6> 04 25 00 00 00 00 01 5d c3 0f 1f 44 00 00 55 31 c0 c7 05 7e [1]kdb> summary sysname Linux release 3.10.84 version #1 SMP Tue Jul 28 19:53:37 IST 2015 machine x86_64 nodename localhost.localdomain domainname (none) ccversion CCVERSION date 2015-12-30 14:07:49 tz_minuteswest 0 uptime 00:01 load avg 0.95 0.21 0.06 MemTotal: 2050340 kB MemFree: 1775224 kB Buffers: 764 kB [1]kdb> bt Stack traceback for pid 2352 0xffff880077275a90 2352 629 1 1 R 0xffff880077276070 *bash ffff880076495e80 0000000000000018 ffff880076495eb8 ffffffff8134b312 0000000000000002 00007f53aec0a000 ffff880076495f50 0000000000000002 0000000000000000 ffff880076495ed8 ffffffff8134b80a 00007f53aec0a000 Call Trace: [<ffffffff8134b312>] ? __handle_sysrq+0xa2/0x170 [<ffffffff8134b80a>] ? write_sysrq_trigger+0x4a/0x50 [<ffffffff811fb61d>] ? proc_reg_write+0x3d/0x80 [<ffffffff811993bd>] ? vfs_write+0xbd/0x1e0 [<ffffffff81199d89>] ? SyS_write+0x49/0xa0 [<ffffffff815a27c7>] ? tracesys+0xdd/0xe2 [1]kdb> rd ax: 000000000000000f bx: ffffffff8190dbc0 cx: ffff88007fd0eec0 dx: 0000000000000000 si: 0000000000000000 di: 0000000000000063 bp: ffff880076495e80 sp: ffff880076495e80 r8: ffffffff81b9069c r9: 0000000000000245 r10: 0000000000000244 r11: 0000000000000003 r12: 0000000000000063 r13: 0000000000000246 r14: 0000000000000007 r15: 0000000000000000 ip: ffffffff8134abb6 flags: 00010096 cs: 00000010 ss: 00000018 ds: 00000018 es: 00000018 fs: 00000018 gs: 00000018 [1]kdb> go Catastrophic error detected kdb_continue_catastrophic=0, type go a second time if you really want to continue [1]kdb> go Catastrophic error detected kdb_continue_catastrophic=0, attempting to continue [ 28.964025] Modules linked in: ip6t_rpfilter ip6t_REJECT ipt_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw iptable_filter snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm snd_page_alloc snd_timer snd serio_raw pcspkr i2c_piix4 virtio_balloon soundcore nfsd auth_rpcgss nfs_acl lockd sunrpc ip_tables xfs libcrc32c ata_generic pata_acpi ata_piix cirrus syscopyarea sysfillrect sysimgblt drm_kms_helper ttm virtio_net virtio_blk drm libata virtio_pci virtio_ring virtio i2c_core floppy dm_mirror dm_region_hash dm_log dm_mod [ 112.090263] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007 [ 112.090263] task: ffff880077275a90 ti: ffff880076494000 task.ti: ffff880076494000 [ 112.090263] RIP: 0010:[<ffffffff8134abb6>] [<ffffffff8134abb6>] sysrq_handle_crash+0x16/0x20 [ 112.090263] RSP: 0018:ffff880076495e80 EFLAGS: 00010096 [ 112.090263] RAX: 000000000000000f RBX: ffffffff8190dbc0 RCX: ffff88007fd0eec0 [ 112.090263] RDX: 0000000000000000 RSI: ffff88007fd0d368 RDI: 0000000000000063 [ 112.090263] RBP: ffff880076495e80 R08: ffffffff81b9069c R09: 0000000000000245 [ 112.090263] R10: 0000000000000244 R11: 0000000000000003 R12: 0000000000000063 [ 112.090263] R13: 0000000000000246 R14: 0000000000000007 R15: 0000000000000000 [ 112.090263] FS: 00007f53aec0c740(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000 [ 112.090263] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 112.090263] CR2: 0000000000000000 CR3: 00000000764bd000 CR4: 00000000000006e0 [ 112.090263] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 112.104034] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 112.104034] Stack: [ 112.104034] ffff880076495eb8 ffffffff8134b312 0000000000000002 00007f53aec0a000 [ 112.104034] ffff880076495f50 0000000000000002 0000000000000000 ffff880076495ed8 [ 112.104034] ffffffff8134b80a 00007f53aec0a000 ffff88007661c000 ffff880076495ef8 [ 112.104034] Call Trace: [ 112.104034] [<ffffffff8134b312>] __handle_sysrq+0xa2/0x170 [ 112.104034] [<ffffffff8134b80a>] write_sysrq_trigger+0x4a/0x50 [ 112.104034] [<ffffffff811fb61d>] proc_reg_write+0x3d/0x80 [ 112.104034] [<ffffffff811993bd>] vfs_write+0xbd/0x1e0 [ 112.104034] [<ffffffff81199d89>] SyS_write+0x49/0xa0 [ 112.104034] [<ffffffff815a27c7>] tracesys+0xdd/0xe2 [ 112.104034] Code: eb 9b 45 01 f4 45 39 65 34 75 e5 4c 89 ef e8 02 f8 ff ff eb db 0f 1f 44 00 00 55 c7 05 20 17 54 00 01 00 00 00 48 89 e5 0f ae f8 <c6> 04 25 00 00 00 00 01 5d c3 0f 1f 44 00 00 55 31 c0 c7 05 7e [ 112.104034] RIP [<ffffffff8134abb6>] sysrq_handle_crash+0x16/0x20 [ 112.104034] RSP <ffff880076495e80> [ 112.104034] CR2: 0000000000000000 [ 112.104034] ---[ end trace 4484e44d0167e21c ]--- [ 112.104034] Kernel panic - not syncing: Fatal exception PANIC: Fatal exception Entering kdb (current=0xffff880077275a90, pid 2352) on processor 1 due to Keyboard Entry [Note:] kdb command "go" is used to continue kernel execution. In above case it will not take you back to bash shell. :) Few questions for you; [Q:1] What exactly you are trying to achieve ? [Q:2] What is the exact issue ? Regards, BKS [[1]] http://people.redhat.com/anderson/crash_whitepaper/#INVOCATION [[2]] https://www.kernel.org/pub/linux/kernel/people/jwessel/kdb/