RFR(M): 8139864: Improve handling of stack protection zones.
Lindenmaier, Goetz
goetz.lindenmaier at sap.com
Fri Nov 27 09:28:17 UTC 2015
Hi David,
thanks for looking at this change!
I edited the thinks you remarked, thanks for spotting that.
I'll run the change through our testing to assure I catch all
issues with jtreg. We have some systems with other page sizes.
Best regards,
Goetz.
> -----Original Message-----
> From: David Holmes [mailto:david.holmes at oracle.com]
> Sent: Freitag, 27. November 2015 06:33
> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; Coleen Phillimore
> (coleen.phillimore at oracle.com) <coleen.phillimore at oracle.com>; hotspot-
> runtime-dev at openjdk.java.net
> Subject: Re: RFR(M): 8139864: Improve handling of stack protection zones.
>
> Hi Goetz,
>
> On 26/11/2015 1:55 AM, Lindenmaier, Goetz wrote:
> > Hi,
> >
> > For a description of the problem see
> https://bugs.openjdk.java.net/browse/JDK-8139864
> >
> > This is a first version of my implementation of the proposal '3' that was
> discussed here:
> > http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2015-
> October/016085.html
> > which is continued here
> > http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2015-
> November/016805.html
> >
> > Opposed to my original proposal, I did not introduce new flags. I
> documented the
> > old flags to specify 4K pages, and save the ergonomic values in static fields
> of JavaThread.
> > This avoids two sets of similar flags.
>
> That seems like a good compromise. Though not sure about placement in
> JavaThread when everything else stack-related seems to be in os class.
>
> > To simplify reviewing, I made two webrevs for the first round:
> > The basic changes to determining the sizes of the zones to protect are in
> this partial webrev:
> > http://cr.openjdk.java.net/~goetz/webrevs/8139864-
> StackZones/webrev.00-basic/
> > This contains the functional change.
>
> This seems okay to me - though I don't claim expertise in this area.
>
> A couple of minor nits:
>
> src/share/vm/runtime/thread.hpp
>
> 1364 static size_t stack_yellow_zone_size() {
> 1365 assert(_stack_red_zone_size > 0, "Don't call this before the
> field is initialized.");
>
> The assert should check yellow size
>
> 1383 static size_t stack_shadow_zone_size() {
> 1384 assert(_stack_red_zone_size > 0, "Don't call this before the
> field is initialized.");
>
> The assert should check shadow size.
>
> ---
>
> src/share/vm/runtime/globals.hpp
>
> kB -> KB
>
> > I also fixed the bounds of ThreadStackSize and CompilerThreadStackSize
> which
> > allowed to specify stacks >> max_intx.
>
> Ok - not sure how this was missed given we do the same for
> VMThreadStackSize :)
>
>
> > If we agree on this, I need to replace all occurrences of the three flags by
> accessor calls.
> > This allows to simplify all the platform code which computed the space
> required
> > over and over again:
> > http://cr.openjdk.java.net/~goetz/webrevs/8139864-
> StackZones/webrev.00-spread/
>
> That all seems okay to me.
>
> > Actually I think there is no need that the shadow zone is page aligned.
> There are no
> > pages to allocate or protect. The size of this zone is only used for banging.
> In most
> > places only the upper bound of the zone is banged. In few places, all pages
> within
> > this zone are banged. But this code also does not depend on a page
> aligned size.
> > Removing the rounding to page sizes here could free up stack space for real
> usage.
> > But I think that should be done in an extra change.
> >
> > I also fixed the bounds of ThreadStackSize and CompilerThreadStackSize
> which
> > allowed to specify stacks >> max_intx.
> >
> > If this is agreed on, I will check for jtreg tests that fail on systems with stack
> > pages > 4K and add the fixes to this change.
>
> You may also need to check the tests for valid command-line args given
> the range adjustments on the stack sizes.
>
> Thanks,
> David
> -----
>
> > Best regards,
> > Goetz.
> >
> >
> >
> >
> >
> >
> >
> >
> >
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