[rrd-users] Valgrind error rrd_update.c:982

Tobias Oetiker tobi at oetiker.ch
Mon Jun 16 10:03:24 CEST 2014 

Hi Mattias,

I have created an issue on github:

https://github.com/oetiker/rrdtool-1.x/issues/504

cheers
tobi

Today Tobias Oetiker wrote:

> Today Matthias Nagel wrote:
>
> > Hi,
> > > care to provide a patch ?
> > I will see what I can do after I got my own application (the one that
> > uses rrdlib) running.
>
> thinking of  it, I might actually have someone who might be
> interested in doing it ...
>
> so check back before you do anything
>
> cheers
> tobi
>
> > Matthias
> >
> > 2014-06-16 9:50 GMT+02:00 Tobias Oetiker <tobi at oetiker.ch>:
> > > Hi Matthias,
> > >
> > > Today Matthias Nagel wrote:
> > >
> > >> Hi,
> > >>
> > >> > The setlocale() thread-safeness problems are well known, but there is also a
> > >> > rather significant lack of a decent widely adopted workaround.
> > >>
> > >> I know, but what I want to say is that according to this page [1] the
> > >> rrd_update_r function is said to be thread-save but it isn't. Hence,
> > >> if I had not stumbled across the first point (aka the memory bug) I
> > >> would not have noticed this one. I  would never have assumed that
> > >> rrd_update_r uses setlocale. (Perhaps sometimes later in the future
> > >> after I would have observed strange behaviour.) That's why I asked for
> > >> a big warning at [1].
> > >>
> > >> I do not know yet, if setlocale is the only problem with rrd_update_r,
> > >> but at least I see a bug fix for this one. There is no need to use
> > >> setlocale at all, if there was an interface like
> > >>
> > >> rrd_update_r( cont char* rrdFile, time_t ts, size_t argc, const char*
> > >> desc[], const T* val[] )
> > >>
> > >> for T being a numeric type. This way one could avoid the conversion to
> > >> and from a string at all. The calling application is responsible of
> > >> providing the correct datatype. That should even simplify rrd_update_r
> > >> because there is no need to
> > >> parse an argument of the pattern "<ts>:<val 1>:...:<val n>".
> > >
> > > since all we are doing with setlocale in rrdtool, is to get strtod to be
> > > NOT locale sensitive. Another aproach would be to switch to a
> > > nonlocale sensitive implementation of strtod and get rid of all the
> > > setlocale calls.
> > >
> > > http://www.jbox.dk/sanos/source/lib/strtod.c.html
> > >
> > > care to provide a patch ?
> > >
> > > cheers
> > > tobi
> > >
> > >
> > >> Regards, Matthias
> > >>
> > >> [1] http://oss.oetiker.ch/rrdtool/prog/rrdthreads.en.html
> > >>
> > >> 2014-06-16 1:47 GMT+02:00 Donovan Baarda <abo at minkirri.apana.org.au>:
> > >> > The setlocale() thread-safeness problems are well known, but there is also a
> > >> > rather significant lack of a decent widely adopted workaround. This is the
> > >> > problem with many of the standard C libraries... they pre-date threading,
> > >> > and there was never consensus/standardizing on any thread safe alternative.
> > >> >
> > >> > For any thread-safe alternative to work, everything needs to use it, but
> > >> > without a standard, you can pretty much guarantee that something you link
> > >> > will not use it, and some platforms won't even have it.
> > >> >
> > >> > So instead, your best option is often to just declare your code
> > >> > non-thread-safe and recommend subprocesses instead... but then the
> > >> > inter-process communication libs are not as well developed as the threading
> > >> > libs.
> > >> >
> > >> > Either that or completely embrace something like glib which replaces nearly
> > >> > everything in the standard C libs and only use other libs that also use
> > >> > glib. When you do this you also have to accept that your code doesn't look
> > >> > like normal C any more, and you might have some platform restrictions.
> > >> >
> > >> >
> > >> >
> > >> > On 16 June 2014 08:39, Matthias Nagel <matthias.h.nagel at gmail.com> wrote:
> > >> >>
> > >> >> Hello,
> > >> >> thanks. In the meantime I patched my Debian packages locally. But I ran
> > >> >> into another race condition. rrd_update_r() isn't thread-save, because the C
> > >> >> locale is an application wide variable. Assume one has rrdlib (A) and some
> > >> >> other library (B) and the execution order is as follows:
> > >> >>
> > >> >> (A1) old_locale = setlocale(...)
> > >> >> (B1) old_locale = setlocale(...)
> > >> >> (A2) // do some locale-dependent stuff
> > >> >> (A3) setlocale( old_locale )
> > >> >> (B2) // do some locale-dependent stuff
> > >> >> (B3) setlocale( old_locale )
> > >> >>
> > >> >> Here, library B can be any library that also sets the global C locale
> > >> >> within a different thread context. In the best case some strings are
> > >> >> misinterpreted, in the worst case the memory gets corrupted :-( At the
> > >> >> moment, I wrote a work-around by using an application wide mutex that must
> > >> >> be locked by any thread that wants to call any library that might change the
> > >> >> global C locale. But of course this isn't very nice.
> > >> >>
> > >> >> Are there any chances that the rrd_update_r function (and relatives) will
> > >> >> be rewritten? For example, C++ locales are bounded to a specific stream and
> > >> >> are not global. At least there should be big, BIG warning at
> > >> >> http://oss.oetiker.ch/rrdtool/prog/rrdthreads.en.html that the C locale is
> > >> >> subject to a race condition.
> > >> >>
> > >> >> Regards, Matthias
> > >> >>
> > >> >> Am Sonntag, 15. Juni 2014, 22:37:01 schrieb Tobias Oetiker:
> > >> >> > Hi Matthias,
> > >> >> >
> > >> >> > yes you are right ... we fixed this in master, but not in the 1.4
> > >> >> > branch ... it is now ...
> > >> >> >
> > >> >> > cheers
> > >> >> > tobi
> > >> >> >
> > >> >> > Today Matthias Nagel wrote:
> > >> >> >
> > >> >> > > Hello,
> > >> >> > >
> > >> >> > > I am writing a multi-threaded C++ application that uses rrdlib
> > >> >> > > natively by calling rrd_update_r().  If I compile without optimazations and
> > >> >> > > enable -ggdb everything seems to work fine. As soon as I switch to -O2 and
> > >> >> > > disable -ggdb my apllication crashes at runtime.
> > >> >> > >
> > >> >> > > If it crashes the output is either
> > >> >> > >
> > >> >> > > *** glibc detected *** rrdtool: <something>
> > >> >> > >
> > >> >> > > or
> > >> >> > >
> > >> >> > > expected timestamp not found in data source from <input>
> > >> >> > >
> > >> >> > > but <input> is not the string that was given to rrd_update_r but
> > >> >> > > unreadable garbage. Obviously, it is a memory corruption problem. Therefore,
> > >> >> > > I ran the application under valgrind and I noticed that the problems comes
> > >> >> > > from inside of the rrdlib. The message is
> > >> >> > >
> > >> >> > >
> > >> >> > > ==11724== Invalid read of size 1
> > >> >> > > ==11724==    at 0x4C2A051: __GI_strcmp (mc_replace_strmem.c:712)
> > >> >> > > ==11724==    by 0x5A4FF7F: setlocale (setlocale.c:210)
> > >> >> > > ==11724==    by 0x505D06B: _rrd_update (rrd_update.c:982)
> > >> >> > > ==11724==  Address 0x9deb0d0 is 0 bytes inside a block of size 12
> > >> >> > > free'd
> > >> >> > > ==11724==    at 0x4C27D4E: free (vg_replace_malloc.c:427)
> > >> >> > > ==11724==    by 0x5A4FCBD: setname (setlocale.c:173)
> > >> >> > > ==11724==    by 0x5A500B0: setlocale (setlocale.c:417)
> > >> >> > > ==11724==    by 0x505D02D: _rrd_update (rrd_update.c:974)
> > >> >> > >
> > >> >> > > Let's have a look at it:
> > >> >> > >
> > >> >> > > rrd_update.c:973: old_locale = setlocale(LC_NUMERIC, NULL);
> > >> >> > > rrd_update.c:974: setlocale(LC_NUMERIC, "C");
> > >> >> > > rrd_update.c:982: setlocale(LC_NUMERIC, old_locale);
> > >> >> > >
> > >> >> > > The problem is obvious. The variable "old_locale" that is used at the
> > >> >> > > 3rd line was assigned at the 1st line. But the 2nd call to "setlocale" freed
> > >> >> > > the return value of the first call. According to the man pages the return
> > >> >> > > value is a pointer to static memory and freed/allocated on every call.
> > >> >> > > Actually the 2nd line (974) should be ommited and it should be
> > >> >> > >
> > >> >> > > rrd_update.c:973: old_locale = setlocale(LC_NUMERIC, "C" );
> > >> >> > > rrd_update.c:974: // deleted
> > >> >> > > rrd_update.c:982: setlocale(LC_NUMERIC, old_locale);
> > >> >> > >
> > >> >> > > Why this double call to "setlocale" anyway?
> > >> >> > >
> > >> >> > > Best regards, Matthias
> > >> >> > >
> > >> >> > >
> > >> >> >
> > >> >> >
> > >> >>
> > >> >> --
> > >> >> Matthias Nagel
> > >> >> Parkstraße 27
> > >> >> 76131 Karlsruhe
> > >> >>
> > >> >> Festnetz: +49-721-96869289
> > >> >> Mobil: +49-151-15998774
> > >> >> e-Mail: matthias.h.nagel at gmail.com
> > >> >> ICQ: 499797758
> > >> >> Skype: nagmat84
> > >> >>
> > >> >> _______________________________________________
> > >> >> rrd-users mailing list
> > >> >> rrd-users at lists.oetiker.ch
> > >> >> https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
> > >> >>
> > >> >
> > >> >
> > >> >
> > >> > --
> > >> > Donovan Baarda <abo at minkirri.apana.org.au>
> > >>
> > >>
> > >>
> > >>
> > >
> > > --
> > > Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
> > > www.oetiker.ch tobi at oetiker.ch +41 62 775 9902
> >
> >
> >
> >
>
>

-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
www.oetiker.ch tobi at oetiker.ch +41 62 775 9902

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