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