RFR(M): 8141529: Fix handling of _JAVA_SR_SIGNUM (original) (raw)

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 JAVASRSIGNUM

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 osaix.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 JAVASRSIGNUM > > > > 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/osaix.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 ? > > > > +sigsett os::Aix::sigs = { 0 }; > > > > I would not initialize the signal set this way. sigsett 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/osaix.hpp.udiff.html > > > > + static struct sigaction sigact[NSIG]; // saved preinstalled sigactions > > + static sigsett 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 osaix.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 osaix.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/osbsd.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 osbsd.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 ossolaris.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. > sigsett is >> NSIG on linux, so it's no good idea to use it there. > > > > Why do we not do this on all platforms, provided sigsett 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 JAVASRSIGNUM > > > > 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 > oslinux, 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 JAVASRSIGNUM > > >> > > >> 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 JAVASRSIGNUM 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 JAVASRSIGNUM > > >> 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::setoursigflags. > > >>> > > >>> 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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