[Bug runtime/13714] New: panic when sampling backtrace() in timer.profile

["brendan.gregg at joyent dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=13714

             Bug #: 13714
           Summary: panic when sampling backtrace() in timer.profile
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap@sourceware.org
        ReportedBy: brendan.gregg@joyent.com
    Classification: Unclassified


The kernel can panic when profiling stack traces on Fedora 16.

window1 (sample workload):

# while :; do tar cf /dev/null /usr; done

window2 (profiling):

# stap -D MAXTRACE=100 -D MAXSTRINGLEN=4096 -ve 'global s; probe timer.profile
{ s[backtrace()] <<< 1; } probe end { foreach (i in s+) { print_stack(i);
printf("\t%d\n", @count(s[i])); } }'

This was tried about a dozen times, and paniced on four of them.

The system had kdump configured and collected a crash dump.  Some details:

# crash /var/crash/2012-02-19-23\:08/vmcore
/usr/lib/debug/lib/modules/3.2.6-3.fc16.x86_64/vmlinux
[...]
      KERNEL: /usr/lib/debug/lib/modules/3.2.6-3.fc16.x86_64/vmlinux
    DUMPFILE: /var/crash/2012-02-19-23:08/vmcore
        CPUS: 1
        DATE: Sun Feb 19 15:04:50 2012
      UPTIME: 00:05:41
LOAD AVERAGE: 1.39, 0.78, 0.32
       TASKS: 72
    NODENAME: 9d219ce8-cf52-409f-a14a-b210850f3231
     RELEASE: 3.2.6-3.fc16.x86_64
     VERSION: #1 SMP Mon Feb 13 20:35:42 UTC 2012
     MACHINE: x86_64  (2393 Mhz)
      MEMORY: 1 GB
       PANIC: "[  341.694043] Oops: 0000 [#1] SMP " (check log for details)
         PID: 3922
     COMMAND: "tar"
        TASK: ffff880037878000  [THREAD_INFO: ffff88001783e000]
         CPU: 0
       STATE: TASK_RUNNING (PANIC)
[...]
crash> bt -a
PID: 3922   TASK: ffff880037878000  CPU: 0   COMMAND: "tar"
 #0 [ffff88003fc037b0] machine_kexec at ffffffff81038bda
 #1 [ffff88003fc03820] crash_kexec at ffffffff810b8482
 #2 [ffff88003fc038f0] oops_end at ffffffff815e2b08
 #3 [ffff88003fc03920] no_context at ffffffff815d6a05
 #4 [ffff88003fc03980] __bad_area_nosemaphore at ffffffff815d6bdd
 #5 [ffff88003fc039e0] bad_area_nosemaphore at ffffffff815d6c0f
 #6 [ffff88003fc039f0] do_page_fault at ffffffff815e55e6
 #7 [ffff88003fc03b00] page_fault at ffffffff815e20b5
    [exception RIP: get_uleb128+83]
    RIP: ffffffffa00773f3  RSP: ffff88003fc03bb8  RFLAGS: 00010046
    RAX: 0000000000000000  RBX: 0000000000000000  RCX: 0000000000000000
    RDX: 0000000000000007  RSI: ffffffffffffffff  RDI: ffff88003fc03bf0
    RBP: ffff88003fc03bb8   R8: 0000000000000030   R9: 0000000000000007
    R10: 0000000000000001  R11: 0000000000000040  R12: ffff88003aae1088
    R13: ffff88001783ffd8  R14: 0000000000000000  R15: ffff88003aae1088
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0000
 #8 [ffff88003fc03bc0] compute_expr at ffffffffa007c63f
[stap_ddfda8cbbf4994e727c76bf533732ecf_3874]
 #9 [ffff88003fc03c70] unwind_frame at ffffffffa007df6c
[stap_ddfda8cbbf4994e727c76bf533732ecf_3874]
#10 [ffff88003fc03dc0] probe_1993 at ffffffffa007fcc6
[stap_ddfda8cbbf4994e727c76bf533732ecf_3874]
#11 [ffff88003fc03e40] enter_profile_probes at ffffffffa007b2c5
[stap_ddfda8cbbf4994e727c76bf533732ecf_3874]
#12 [ffff88003fc03e70] profile_tick at ffffffff81098ea9
#13 [ffff88003fc03e90] tick_sched_timer at ffffffff810a0e4e
#14 [ffff88003fc03ec0] __run_hrtimer at ffffffff81093e90
#15 [ffff88003fc03f20] hrtimer_interrupt at ffffffff8109480b
#16 [ffff88003fc03f90] smp_apic_timer_interrupt at ffffffff815ec589
#17 [ffff88003fc03fb0] apic_timer_interrupt at ffffffff815ea45e
--- <IRQ stack> ---
#18 [ffff88001783fed0] apic_timer_interrupt at ffffffff815ea45e
    RIP: ffffffffffffff10  RSP: 0000000000000203  RFLAGS: 00000010
    RAX: ffff88003fc13780  RBX: 00000000008c2ed0  RCX: 0000000000000000
    RDX: ffff88001783e000  RSI: 0000000000000008  RDI: ffff88001783ff78
    RBP: ffffffff8119691f   R8: 0000000000000001   R9: 0000000000000001
    R10: 0000000000000001  R11: ffffffff811839f2  R12: ffff88001783fef8
    R13: 00007fff549ffff0  R14: ffff88001783ff40  R15: ffffffff81196824
    ORIG_RAX: 000000000000fe2e  CS: ffffffff815e1e8d  SS: ffff88001783ff88
bt: WARNING: possibly bogus exception frame
crash> dis get_uleb128+83
0xffffffffa00773f3 <get_uleb128+83>:    movzbl (%rdx),%r10d

Version and system details:

# stap -V
Systemtap translator/driver (version 1.6/0.152 non-git sources)
Copyright (C) 2005-2011 Red Hat, Inc. and others
This is free software; see the source for copying conditions.
enabled features: AVAHI LIBRPM LIBSQLITE3 NSS BOOST_SHARED_PTR
TR1_UNORDERED_MAP NLS
# uname -a
Linux 9d219ce8-cf52-409f-a14a-b210850f3231 3.2.6-3.fc16.x86_64 #1 SMP Mon Feb
13 20:35:42 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
# cat /etc/redhat-release 
Fedora release 16 (Verne)

This is Fedora as a guest running under KVM.  SystemTap was installed via yum.

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