dtrace ustack kernel panic

[Andriy Gapon]

on 03/08/2011 11:42 Andriy Gapon said the following:
> on 03/08/2011 03:47 maestro something said the following:
>> now it seems that the ustack() action on i386 and FreeBSD-9.0BETA1 almost works.
>>
>> Almost because dtrace still exits (this time without an error message) The
>> process for which the ustack should be genereated is terminated
>> Here are the specifics:
>>
>> fb90i386# dtrace -n 'syscall::accept:return / execname == "nc" / { ustack();}'
>> dtrace: description 'syscall::accept:return ' matched 1 probe
>> CPU     ID                    FUNCTION:NAME
>>   0  46457                    accept:return
>>               libc.so.7`__sys_accept+0x7
>>               0x3
>>               0xed96e824
>>
>>
>> This alsmost looks like a stack trace I'd say
>> However, dtrace quits once I connect to nc
>>
>> nc quits with the following error message
>>
>> fb90i386# nc -vl 4444
>> nc: Polling Error: Interrupted system call
> 
> This could be a combination of several factors.
> First, for some reason nc gets EINTR in one of its system calls (poll(2)).
> Second, nc treats EINTR as a serious error and exits.

Looks like nc gets EINTR when dtrace does ptrace(PT_CONTINUE).
So this is the culprit for your test case.

> Third, this is what happens on the dtrace side:

Recorded dtrace behavior seems to be correct.

>  30495 100974 dtrace   CALL  write(0x1,0x8035c2000,0x1a)
>  30495 100974 dtrace   GIO   fd 1 wrote 26 bytes
>        "libc.so.7`__sys_accept+0xc"
>  30495 100974 dtrace   RET   write 26/0x1a
>  30495 100974 dtrace   CALL  write(0x1,0x8035c2000,0x1)
>  30495 100974 dtrace   GIO   fd 1 wrote 1 byte
>        "
>        "
>  30495 100974 dtrace   RET   write 1
>  30495 100974 dtrace   CALL  thr_kill(0x1c129,SIGUSR1)
>  30495 100974 dtrace   RET   thr_kill 0
>  30495 100974 dtrace   CALL  ptrace(PT_IO,0x771e,0x7fffffffbb10,0)
>  30495 100974 dtrace   RET   ptrace 0
>  30495 100974 dtrace   CALL  ptrace(PT_IO,0x771e,0x7fffffffbb10,0)
>  30495 114985 dtrace   RET   _umtx_op -1 errno 4 Interrupted system call
>  30495 100974 dtrace   RET   ptrace 0
>  30495 114985 dtrace   PSIG  SIGUSR1 caught handler=0x80085d610 mask=0x5ffefedf
> code=0x10007
>  30495 100974 dtrace   CALL  _umtx_op(0x802007668,0x15,0x1,0,0)
>  30495 114985 dtrace   CALL  sigprocmask(SIG_SETMASK,0x7fffffbfd9fc,0)
>  30495 100974 dtrace   RET   _umtx_op 0
>  30495 114985 dtrace   RET   sigprocmask 0
>  30495 100974 dtrace   CALL  _umtx_op(0x800a71778,0xf,0,0,0)
>  30495 114985 dtrace   CALL  sigreturn(0x7fffffbfd630)
>  30495 114985 dtrace   RET   sigreturn JUSTRETURN
>  30495 114985 dtrace   CALL  ptrace(PT_CONTINUE,0x771e,0x1,0)
>  30495 114985 dtrace   RET   ptrace 0
>  30495 114985 dtrace   CALL  ptrace(PT_IO,0x771e,0x7fffffbfdee0,0)
>  30495 114985 dtrace   RET   ptrace -1 errno 16 Device busy
>  30495 114985 dtrace   CALL  _umtx_op(0x80200d668,0x15,0x1,0,0)
>  30495 114985 dtrace   RET   _umtx_op 0
>  30495 114985 dtrace   CALL  madvise(0x803c52000,0x11000,MADV_FREE)
>  30495 114985 dtrace   RET   madvise 0
>  30495 114985 dtrace   CALL  madvise(0x803c1d000,0x14000,MADV_FREE)
>  30495 114985 dtrace   RET   madvise 0
>  30495 114985 dtrace   CALL  madvise(0x803c07000,0x1000,MADV_FREE)
>  30495 114985 dtrace   RET   madvise 0
>  30495 114985 dtrace   CALL  madvise(0x8037fc000,0x2000,MADV_FREE)
>  30495 114985 dtrace   RET   madvise 0
>  30495 114985 dtrace   CALL  madvise(0x8037f2000,0x8000,MADV_FREE)
>  30495 114985 dtrace   RET   madvise 0
>  30495 114985 dtrace   CALL  madvise(0x8037f0000,0x1000,MADV_FREE)
>  30495 100974 dtrace   RET   _umtx_op 0
>  30495 114985 dtrace   RET   madvise 0
>  30495 100974 dtrace   CALL  ptrace(PT_DETACH,0x771e,0,0)
>  30495 114985 dtrace   CALL  madvise(0x8037e0000,0x9000,MADV_FREE)
>  30495 100974 dtrace   RET   ptrace -1 errno 3 No such process
> 
> Looks like something fishy happens when that SIGUSR1 is generated.
> I wish a dtrace-for-userland expert and/or a ptrace(2) expert could help us here.
> 


-- 
Andriy Gapon