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Re: Read fault when running example network/nfsd-trace.stp stap


Hmm. The good news here is that systemtap is properly exiting here
instead of accessing that NULL pointer and crashing your system.

Does this work for a while then fail or does it always fail on the
first read request?

I'm not sure what is going on here, the syntax looks reasonable.

(BTW, it doesn't matter that ex_path is a struct path and not a
pointer, in systemtap you always use '->' in script code.)

On Fri, May 26, 2017 at 9:59 AM, Yun-Chih Chen <b03902074@ntu.edu.tw> wrote:
> I am running the example NFS stap file network/nfsd-trace.stp[1] on a
> NFS server.
> The stap file fails with the following message when a new NFS read
> request comes in:
>
> # sudo stap -v nfsd-trace.stp
> Pass 1: parsed user script and 467 library scripts using
> 138276virt/44988res/7568shr/37488data kb, in 130usr/20sys/154real ms.
> Pass 2: analyzed script: 22 probes, 66 functions, 9 embeds, 1 global
> using 342304virt/246608res/9036shr/241516data kb, in
> 6020usr/730sys/6779real ms.
> Pass 3: translated to C into
> "/tmp/stapoyPncz/stap_b12e64c3fc1fc31297eb3b8c93c2dacf_107403_src.c"
> using 342304virt/246856res/9228shr/241516data kb, in
> 200usr/70sys/265real ms.
> Pass 4: compiled C into
> "stap_b12e64c3fc1fc31297eb3b8c93c2dacf_107403.ko" in
> 4230usr/880sys/5113real ms.
> Pass 5: starting run.
> ERROR: read fault [man error::fault] at 0x0000000000000040 (addr) near
> operator '->' at nfsd-trace.stp:18:31
>
> It says "fh->fh_export->ex_path->mnt" is probably a reference on null
> pointer ....
>
> The test is conducted on both Linux 4.10 on Fedora 25 and Linux 3.10
> on CentOS 7.  Both fails at the same place.
> Does anyone know what's going on here?
>
> Thanks,
>
>
> Yunchih
>
> [1] https://sourceware.org/systemtap/examples/network/nfsd-trace.stp



-- 
David Smith
Principal Software Engineer
Red Hat


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