[lttng-dev] Getting SIGBUS in babeltrace - occasionally

Amit Margalit AMITM at il.ibm.com
Wed Jul 24 10:48:17 EDT 2013


Access beyond end of file seems to be the issue IIUC.

Let me try to give as much context as I can and answer your questions one 
by one:


lttng-ust 2.2.0, lttng-tools 2.2.0, babeltrace - I used git hash 
cc26a15ac355d886bb507955fdaec9b218024713 with a patch on babeltrace.i.in.

[I cannot supply the patch as this requires my employer's (IBM) approval - 
I am in the process of obtaining a permanent contribution approval, but 
until then...]

However, I can tell you exactly what it does:
1. Adds a typedef for 'ssize_t'
2. Added a call to _bt_ctf_get_decl_from_def() around the argument 
supplied to _bt_ctf_get_int_len()
3. Changed all use of {} in string ".format()" calls to add numbers (e.g. 
{0} instead of {}) - as this doesn't work for Python 2.6.

I am waiting for the contribution approval and then I'll submit a patch.

To provide a trace sample, I'll need a special approval, which could take 
very long.

System Setup

Processor: Xeon-family 6-cores (12 if you count HT)
RAM: 24GB of RAM, page size is 4KB.
OS: Linux based on an MCP (IBM's SuSE derivative) 

Tracing Setup

Same system used to generate, collect and read the traces.
100% user-space.


This is not readily reproducible. Some context:

We have an in-house trace mechanism including a code instrumentor and a 
curses-based viewer (actually urwid+python).
My current project is to embed LTTng logging and trace capabilites into 
several open-source projects, because we couldn't use our in-house tracer 
without having GPL issues.
I have written a back-end that enables our in-house viewer to display 
Lttng traces, by linking with libbabeltrace (allowed by its LGPL license).

As far as I can tell SIGBUS happens to me when I was doing a search. This 
literally reads the events in sequence and tries to compare some fields 
against some criteria.

And here's the main reason why I think this is happening - I was adding a 
trace (using add_traces_recursive(trace_dir,'ctf')) while the session is 
active (i.e. not stopped).

I can see 2 problematic scenarios here:

Scenario 1

When I add the trace to the context babeltrace performs mmap() according 
to the size of the file(s) at that moment.
The files keep growing.
When I try to access new packets they may lie beyond the end of the 
mmap'ed region. I think this should lead to SIGSEGV and not to SIGBUS.

Scenario 2

Due to buffering issues, I could be having a race with the session daemon, 
where my code reads the beginning of a packet that was already written to 
the file, and try to access the contents, which were not yet written. 
Again - could happen around the end of the file, with the session still 


Amit Margalit
IBM XIV - Storage Reinvented
XIV-NAS Development Team
Tel. 03-689-7774
Fax. 03-689-7230

From:   Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
To:     Amit Margalit/Israel/IBM at IBMIL
Cc:     lttng-dev at lists.lttng.org
Date:   07/24/2013 04:20 PM
Subject:        Re: [lttng-dev] Getting SIGBUS in babeltrace - 

* Mathieu Desnoyers (mathieu.desnoyers at efficios.com) wrote:
> * Amit Margalit (AMITM at il.ibm.com) wrote:
> > Hi,
> > 
> > I am getting occasional SIGBUS inside _aligned_integer_read() in 
> > ./formats/ctf/types/integer.c
> > 
> > Here is the backtrace, maybe someone could take a look and suggest 
> > something:
> It looks like you're hitting the internal checks for overflow on the
> buffer boundaries.

Please forget about my previous email, I'm utterly wrong. That should
teach me to reply before my first morning coffee ;)

We indeed have internal checks for overflows in babeltrace, but those
are not triggering SIGBUS ever, they return failure gracefully.

What seems to happen in your case is documented here:

mmap(2) manpage:

       SIGBUS Attempted access to a portion of the buffer that does not 
              spond  to  the  file  (for  example, beyond the end of the 
              including the case  where  another  process  has  truncated 

I'm curious to learn which versions of babeltrace/ust/modules you are
using, if you modified them (and how), and if you can get us a sample
trace that triggers the issue.

Also, a bit of context about your setup: is this 32-bit or 64-bit
user-space, which OS.


By any chance, is it possible that you record your trace on a platform
with 4kB pages, and run babeltrace on it on a platform having 64kB
pages? Everything points me to include/babeltrace/mmap-align.h
mmap_align_addr(). We might be mmaping beyond the end of file in this



> On which babeltrace version can you reproduce it ? Did you do any
> modification to babeltrace on your own on top ?
> Are you getting this with a lttng-ust or lttng-modules trace ? If yes,
> which version of the tool has generated the trace ?
> Can you provide a sample trace that triggers this issue ?
> Can you give us the detailed sequence of steps you use to reproduce ?
> Thanks,
> Mathieu
> > #0  _aligned_integer_read (definition=0x954320, ppos=0x106e028) at 
> > integer.c:81
> > #1  ctf_integer_read (ppos=0x106e028, definition=0x954320) at 
> > integer.c:224
> > #2  0x00007ffff070e36e in generic_rw (definition=<optimized out>, 
> > pos=0x106e028) at ../include/babeltrace/types.h:133
> > #3  bt_struct_rw (ppos=0x106e028, definition=0x9542e0) at struct.c:56
> > #4  0x00007ffff13f7fda in generic_rw (definition=<optimized out>, 
> > pos=0x106e028) at ../../include/babeltrace/types.h:133
> > #5  ctf_packet_seek (stream_pos=0x106e028, index=<optimized out>, 
> > whence=<optimized out>) at ctf.c:860
> > #6  0x00007ffff070a3f1 in seek_file_stream_by_timestamp 
> > (cfs=cfs at entry=0x106cf90, 
timestamp=timestamp at entry=1374636821498972926) 
> > at iterator.c:141
> > #7  0x00007ffff070aa96 in seek_ctf_trace_by_timestamp 
> > (stream_heap=0x176d310, timestamp=1374636821498972926, tin=<optimized 
> > out>) at iterator.c:188
> > #8  bt_iter_set_pos (iter=iter at entry=0xfdafa0, iter_pos=0x2bf59f0) at 
> > iterator.c:439
> > #9  0x00007ffff1624f01 in _wrap__bt_iter_set_pos (self=<optimized 
> > args=<optimized out>) at babeltrace_wrap.c:3805
> > #10 0x00007ffff7b28c0c in call_function (oparg=<optimized out>, 
> > pp_stack=<optimized out>) at Python/ceval.c:3679
> > #11 PyEval_EvalFrameEx (f=0x1c243c0, throwflag=<optimized out>) at 
> > Python/ceval.c:2370
> > #12 0x00007ffff7b2e0d2 in PyEval_EvalCodeEx (co=0xa8e5d0, 
> > globals=<optimized out>, locals=<optimized out>, args=0x2088cc8, 
> > argcount=0, kws=0x0, kwcount=0, defs=0x0, defcount=0, closure=0x0)
> >     at Python/ceval.c:2942
> > .
> > .
> > .
> > 
> > Any suggestions are welcome.
> > 
> > Amit Margalit
> > IBM XIV - Storage Reinvented
> > XIV-NAS Development Team
> > Tel. 03-689-7774
> > Fax. 03-689-7230
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

Mathieu Desnoyers
EfficiOS Inc.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lttng.org/pipermail/lttng-dev/attachments/20130724/60513d38/attachment-0001.html>

More information about the lttng-dev mailing list