dtrace pid provider on entry == Trace/BPT trap process

[Andreas Longwitz]

Maybe the following is of interest for DTrace experts:

>> I use FreeBSD 10.3-STABLE r317936 with updated /usr/lib/dtrace/ip.c and
>> see an issue that in my opinion should have been solved in r269342:
> 
> 10.3 would be missing a number of other fixes for issues that might
> cause the symptom you're seeing. Unfortunately, userland DTrace is not
> very usable on FreeBSD before 11.0.

I have repeated my looptest on a server running FreeBSD 12.0-CURRENT #0
r324306 with GENERIC kernel. I saw the same problem as described before
for FreeBSD 10.3-Stable r317936:

Nov  7 10:54:09 <kern.info> dssbkp2 kernel: pid 38041 (looptest), uid
1003: exited on signal 5

Further I saw following error message from dtrace:

  dtrace: failed to grab pid 38622: Device busy.

After some minutes playing around the server crashed with

panic: PHOLD of exiting process 0xfffff80004c80540
cpuid = 0
time = 1510051083
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame
0xfffffe0231e22700
vpanic() at vpanic+0x19c/frame 0xfffffe0231e22780
kassert_panic() at kassert_panic+0x126/frame 0xfffffe0231e227f0
uread() at uread+0x173/frame 0xfffffe0231e22830
fasttrap_tracepoint_remove() at fasttrap_tracepoint_remove+0x23/frame
0xfffffe0231e22860
fasttrap_tracepoint_disable() at fasttrap_tracepoint_disable+0x31a/frame
0xfffffe0231e228d0
fasttrap_pid_disable() at fasttrap_pid_disable+0x8e/frame 0xfffffe0231e22910
dtrace_ecb_disable() at dtrace_ecb_disable+0x11c/frame 0xfffffe0231e22940
dtrace_state_destroy() at dtrace_state_destroy+0x169/frame
0xfffffe0231e22980
dtrace_dtr() at dtrace_dtr+0x63/frame 0xfffffe0231e229a0
devfs_destroy_cdevpriv() at devfs_destroy_cdevpriv+0x8b/frame
0xfffffe0231e229c0
devfs_close_f() at devfs_close_f+0x65/frame 0xfffffe0231e229f0
closef() at closef+0x1f5/frame 0xfffffe0231e22a80
closefp() at closefp+0x9f/frame 0xfffffe0231e22ac0
amd64_syscall() at amd64_syscall+0x79b/frame 0xfffffe0231e22bf0
Xfast_syscall() at Xfast_syscall+0xfb/frame 0xfffffe0231e22bf0
--- syscall (6, FreeBSD ELF64, sys_close), rip = 0x80128f47a, rsp =
0x7fffffffe878, rbp = 0x7fffffffe890 ---

>> I run a simple program looptest, that loops around a sprintf() call and
>> want to check this program with
>>
>> dtrace -n 'pid$target:libc.so.*::entry {@[probefunc] = count();}' -p
>> $(pgrep looptest)
>> dtrace: description 'pid$target:libc.so.*::entry ' matched 3863 probes
>>
>> After some seconds I hit CTRL-C and see
>>
>>   __vfprintf                                                   741685
>>   localeconv_l                                                 741685
>>   memset                                                       741685
>>   sprintf                                                      741685
>>   vsprintf                                                     741685
>>   __sfvwrite                                                  1483369
>>   memcpy                                                      2225052
>>
>> and at the same time looptest stops with
>>    Trace/BPT trap (Speicherabzug geschrieben)
>> and on the console I see the kernel message
>>    pid 67550 (looptest), uid 1003: exited on signal 5 (core dumped)
>>
>> The trap does not occur all the time, but it is no problem to repeat the
>> trap.


-- 
Andreas Longwitz