RFR(M): 8141529: Fix handling of _JAVA_SR_SIGNUM
Lindenmaier, Goetz
goetz.lindenmaier at sap.com
Tue Nov 17 07:52:37 UTC 2015
David, Dmitry,
I think this is reviewed now. Could one of you please sponsor this?
The final webrev, including a full changeset patch, is this:
http://cr.openjdk.java.net/~goetz/webrevs/8141529-NSIG/webrev.02/
It ran successfully through our nightly tests, tonight.
Best regards,
Goetz.
> -----Original Message-----
> From: Dmitry Samersoff [mailto:dmitry.samersoff at oracle.com]
> Sent: Montag, 16. November 2015 11:53
> To: Lindenmaier, Goetz; Thomas Stüfe
> Cc: David Holmes; hotspot-runtime-dev at openjdk.java.net; serviceability-
> dev
> Subject: Re: RFR(M): 8141529: Fix handling of _JAVA_SR_SIGNUM
>
> Goetz,
>
> Looks good for me.
>
> Thank you for a nice cleanup.
>
> -Dmitry
>
>
> On 2015-11-16 13:25, Lindenmaier, Goetz wrote:
> > Hi Thomas,
> >
> >
> >
> > thanks for looking at this.
> >
> >
> >
> >> MAX2(SIGSEGV, SIGBUS)
> >
> > I really would like to leave the code as-is. This would be a functional
> >
> > change, while I only intend to fix issues in this change. Also, as David
> >
> > explained, it might break for some os implementations.
> >
> >
> >
> >> the only way to initialize it is with one of sigemptyset() or sigfillset().
> >
> > I added initialization with sigemptyset(). Unfortunately, there is no
> > static
> >
> > initializer for this.
> >
> >
> >
> >> I would like to see those removed from os::Aix and put into os_aix.cpp at
> static filescope
> >
> > I moved these to static scope on the three oses.
> >
> >
> >
> > Here is the new webrev:
> >
> > http://cr.openjdk.java.net/~goetz/webrevs/8141529-NSIG/webrev.02/
> >
> >
> >
> > Best regards,
> >
> > Goetz.
> >
> >
> >
> >
> >
> > *From:*Thomas Stüfe [mailto:thomas.stuefe at gmail.com]
> > *Sent:* Freitag, 13. November 2015 10:54
> > *To:* Lindenmaier, Goetz
> > *Cc:* Dmitry Samersoff; David Holmes;
> > hotspot-runtime-dev at openjdk.java.net; serviceability-dev
> > *Subject:* Re: RFR(M): 8141529: Fix handling of _JAVA_SR_SIGNUM
> >
> >
> >
> > Hi Goetz,
> >
> >
> >
> > sorry for not looking at this earlier. This is a nice cleanup. Some remarks:
> >
> >
> >
> > http://cr.openjdk.java.net/~goetz/webrevs/8141529-
> NSIG/webrev.01/src/os/aix/vm/os_aix.cpp.udiff.html
> >
> >
> >
> > + if (sig > MAX2(SIGSEGV, SIGBUS) && // See 4355769.
> >
> > + sig < NSIG) { // Must be legal signal and fit
> > into sigflags[].
> >
> >
> >
> > I do not like much the MAX2() construct. I would like it better to
> > explicitly check whether the SR signal is one of the "forbidden" ones
> > the VM uses.
> >
> >
> >
> > Maybe keep a mask defined centrally for each platform which contains
> > signals the VM needs for itself ?
> >
> >
> >
> > +sigset_t os::Aix::sigs = { 0 };
> >
> >
> >
> > I would not initialize the signal set this way. sigset_t is an opaque
> > type; the only way to initialize it is with one of sigemptyset() or
> > sigfillset().
> >
> >
> >
> > http://cr.openjdk.java.net/~goetz/webrevs/8141529-
> NSIG/webrev.01/src/os/aix/vm/os_aix.hpp.udiff.html
> >
> >
> >
> > + static struct sigaction sigact[NSIG]; // saved preinstalled sigactions
> >
> > + static sigset_t sigs; // mask of signals that have
> >
> >
> >
> > + static int sigflags[NSIG];
> >
> >
> >
> > I know this is not in the scope of your change, but I would like to see
> > those removed from os::Aix and put into os_aix.cpp at static filescope.
> > There is no need at all to export those, and you would get rid of the
> > signal.h dependency you know have when including os_aix.hpp.
> >
> >
> >
> >
> >
> > http://cr.openjdk.java.net/~goetz/webrevs/8141529-
> NSIG/webrev.01/src/os/bsd/vm/jsig.c.udiff.html
> >
> > http://cr.openjdk.java.net/~goetz/webrevs/8141529-
> NSIG/webrev.01/src/os/bsd/vm/os_bsd.cpp.udiff.html
> >
> >
> >
> > On BSD, we have realtime signals.
> >
> >
> >
> > http://fxr.watson.org/fxr/source/sys/signal.h
> >
> > #define SIGRTMAX 126
> >
> > and NSIG does not contain them:
> >
> > #define NSIG 32
> >
> >
> >
> > The max. possible signal number would be 126, which unfortunately does
> > not even fit into a 64bit mask.
> >
> >
> >
> > So the code in jsig.c is broken for the case that someone wants to
> > register realtime signals, if the VM were to ever use realtime signals
> > itself, which now is not the case.
> >
> >
> >
> > The same is true for os_bsd.cpp, where signal chaining will not work if
> > the application did have handler for real time signals pre-installed
> > before jvm is loaded.
> >
> >
> >
> > Solaris:
> >
> >
> >
> > The only platform where NSIG is missing?
> >
> >
> >
> > Here, we calculate the max. signal number dynamically in os_solaris.cpp,
> > presumably because SIGRTMAX is not a constant and can be changed using
> > system configuration. But then, on Linux we have the same situation
> > (SIGRTMAX is dynamic) and there we do not go through the trouble of
> > calculating the max. signal number dynamically. Instead we just use
> > NSIG=64 and rely on the fact that NSIG is larger than the largest
> > possible dynamic value for SIGRTMAX.
> >
> >
> >
> > Solaris does not seem to have NSIG defined, but I am sure there is also
> > a max. possible value for SIGRTMAX (the default seems to be 48). So, one
> > could probably safely define NSIG for Solaris too, so that we have NSIG
> > defined on all Posix platforms.
> >
> >
> >
> >
> >
> > On Thu, Nov 12, 2015 at 8:24 PM, Lindenmaier, Goetz
> > <goetz.lindenmaier at sap.com <mailto:goetz.lindenmaier at sap.com>>
> wrote:
> >
> > Hi David, Dmitry,
> >
> > I've come up with a new webrev:
> > http://cr.openjdk.java.net/~goetz/webrevs/8141529-NSIG/webrev.01/
> >
> > I hit on some more issues:
> > - As proposed, I replaced MAXSIGNUM by NSIG
> > - On AIX, NSIG=255. Therefore storing bits in a word does not work.
> > I'm now using bitset functionality from signal.h as it's done in
> > other places.
> > sigset_t is >> NSIG on linux, so it's no good idea to use it there.
> >
> >
> >
> > Why do we not do this on all platforms, provided sigset_t contains all
> > signals (incl. realtime signals) ?
> >
> >
> >
> > - In the os files I found another bit vector that now is too small:
> > sigs.
> > I adapted that, too. Removed the dead declaration of this on
> > solaris.
> >
> > Best regards,
> > Goetz.
> >
> >
> >
> >
> >
> > Kind Regards, Thomas
> >
> >
> >
> >
> >
> > > -----Original Message-----
> > > From: Dmitry Samersoff [mailto:dmitry.samersoff at oracle.com
> <mailto:dmitry.samersoff at oracle.com>]
> >
> > > Sent: Donnerstag, 12. November 2015 10:05
> > > To: Lindenmaier, Goetz; David Holmes; hotspot-runtime-
> > > dev at openjdk.java.net <mailto:dev at openjdk.java.net>; serviceability-
> dev
> > > Subject: Re: RFR(M): 8141529: Fix handling of _JAVA_SR_SIGNUM
> > >
> > > Goetz,
> > >
> > > *BSD including OS X also defines NSIG (just checked) and if my
> > memory is
> > > not bogus, AIX defines it too.
> > >
> > > So you may consider to use NSIG on all platform.
> > >
> > > -Dmitry
> > >
> > > On 2015-11-12 11:36, Lindenmaier, Goetz wrote:
> > > > OK I'll change it to NSIG. That's used in other places in
> > os_linux, too.
> > > > So it's really more consistent.
> > > >
> > > > Best regards,
> > > > Goetz
> > > >
> > > >> -----Original Message-----
> > > >> From: Dmitry Samersoff [mailto:dmitry.samersoff at oracle.com
> > <mailto:dmitry.samersoff at oracle.com>]
> > > >> Sent: Donnerstag, 12. November 2015 09:22
> > > >> To: David Holmes; Lindenmaier, Goetz; hotspot-runtime-
> > > >> dev at openjdk.java.net <mailto:dev at openjdk.java.net>;
> > serviceability-dev
> > > >> Subject: Re: RFR(M): 8141529: Fix handling of _JAVA_SR_SIGNUM
> > > >>
> > > >> David,
> > > >>
> > > >> I think it's better to use NSIG (without underscore) defined in
> > signal.h
> > > >>
> > > >> -Dmitry
> > > >>
> > > >>
> > > >> On 2015-11-12 10:35, David Holmes wrote:
> > > >>> Hi Goetz,
> > > >>>
> > > >>> Adding in serviceability-dev
> > > >>>
> > > >>> On 9/11/2015 6:22 PM, Lindenmaier, Goetz wrote:
> > > >>>> Hi,
> > > >>>>
> > > >>>> The environment variable _JAVA_SR_SIGNUM can be set to a
> signal
> > > >> number
> > > >>>> do be used by the JVM's suspend/resume mechanism.
> > > >>>>
> > > >>>> If set, a signal handler is installed and the current signal
> > handler
> > > >>>> is saved to an array.
> > > >>>> On linux, this array had size MAXSIGNUM=32, and
> _JAVA_SR_SIGNUM
> > > >> was
> > > >>>> allowed
> > > >>>> to range up to _NSIG=65. This could cause memory corruption.
> > > >>>>
> > > >>>> Further, in jsig.c, an unsinged int is used to set a bit for
> > signals.
> > > >>>> This also
> > > >>>> is too small, as only 32 signals can be supported. Further, the
> > > >>>> signals are mapped
> > > >>>> wrong to these bits. '0' is not a valid signal, but '32'
> > was. 1<<32
> > > >>>> happens to map to
> > > >>>> zero, so the signal could be stored, but this probably was not
> > > >>>> intended that way.
> > > >>>>
> > > >>>> This change increases MAXSIGNUM to 65 on linux, and to 64 on
> > aix. It
> > > >>>> introduces
> > > >>>> proper checking of the signal read from the env var, and issues a
> > > >>>> warning if it
> > > >>>> does not use the signal set. It adapts the data types in jisig.c
> > > >>>> properly.
> > > >>>>
> > > >>>> Please review this change. I please need a sponsor.
> > > >>>> http://cr.openjdk.java.net/~goetz/webrevs/8141529-
> NSIG/webrev.00
> > > >>>
> > > >>> This all sounds very good to me. (I must find out why Solaris
> > is not
> > > >>> involved here :) ).
> > > >>>
> > > >>> On Linux you didn't add the bounds check to
> > os::Linux::set_our_sigflags.
> > > >>>
> > > >>> I'm also wondering about documenting where we are determining
> the
> > > >>> maximum from? Is it simply _NSIG on some/all distributions?
> > And I see
> > > >>> _NSIG is supposed to be the biggest signal number + one. Also
> > linux
> > > >>> defines NSIG = _NSIG so which should we be using?
> > > >>>
> > > >>> Thanks,
> > > >>> David
> > > >>>
> > > >>>> Best regards,
> > > >>>> Goetz.
> > > >>>>
> > > >>
> > > >>
> > > >> --
> > > >> Dmitry Samersoff
> > > >> Oracle Java development team, Saint Petersburg, Russia
> > > >> * I would love to change the world, but they won't give me the
> > sources.
> > >
> > >
> > > --
> > > Dmitry Samersoff
> > > Oracle Java development team, Saint Petersburg, Russia
> > > * I would love to change the world, but they won't give me the
> > sources.
> >
> >
> >
>
>
> --
> Dmitry Samersoff
> Oracle Java development team, Saint Petersburg, Russia
> * I would love to change the world, but they won't give me the sources.
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