RFR(S): 8186286: [BSD] Primary thread's stack size is reported incorrectly

[David Holmes]

Hi Gunter,

On 23/08/2017 11:40 PM, Haug, Gunter wrote:
> Hi David,
> 
> Sorry for the late reply! I have corrected the typos and updated the change, here is the new webrev:
> 
> http://cr.openjdk.java.net/~ghaug/webrevs/8186286.v2

The typos are not fixed in that webrev. ??

> Would you mind sponsoring it?

Sure.

> Re not using os::vm_page_size(): You’re right, and I thought the same - it’s certainly correct for the primary thread. However, os::vm_page_size() isn’t used in the function and I think it’s not much of a problem to call getpagesize() in this particular case.

Ok.

Thanks,
David

> Thanks and best regards,
> Gunter
> 
> 
> 
> On 18.08.17, 06:18, "David Holmes" <david.holmes at oracle.com> wrote:
> 
>      Hi Thomas,
>      
>      On 18/08/2017 1:59 PM, Thomas Stüfe wrote:
>      > Hi David,
>      >
>      > On Thu, Aug 17, 2017 at 11:54 PM, David Holmes <david.holmes at oracle.com
>      > <mailto:david.holmes at oracle.com>> wrote:
>      >
>      >     Hi Gunter,
>      >
>      >     On 18/08/2017 1:01 AM, Haug, Gunter wrote:
>      >
>      >         Thanks for the review, Aleksey and Thomas
>      >
>      >         You’re right, it is much nicer to use the macros. I’ve updated
>      >         the change accordingly:
>      >         http://cr.openjdk.java.net/~ghaug/webrevs/8186286.v1
>      >         <http://cr.openjdk.java.net/~ghaug/webrevs/8186286.v1>
>      >
>      >
>      >     I'm unclear about the logic change here. If you round down then
>      >     there is a chance you will enter the following if-block where
>      >     otherwise you would not.
>      >
>      >       915     *size = align_down(*size, getpagesize());
>      >       916
>      >       917     if ((*size) < (DEFAULT_MAIN_THREAD_STACK_PAGES *
>      >     (size_t)getpagesize())) {
>      >
>      >
>      > I don't see how this could happen? Gunters fix causes the size to snap
>      > to the lower page boundary, but never cross it. The code below ensures a
>      > lower cap at a page boundary.
>      
>      Yes you are right - sorry for the noise.
>      
>      David
>      
>      > If size was larger than that cap, after the align_down it will be at
>      > most right at that cap. If it was lower than the cap, it stays lower. In
>      > both cases behavior  is unchanged.
>      >
>      > Cheers, Thomas
>      >
>      >     Have you verified with a range of aligned and unaligned stack sizes
>      >     around that threshhold that everything works okay?
>      >
>      >     Some typos in the comment block:
>      >
>      >     alligned -> aligned
>      >     boundries -> boundaries
>      >     I round -> We round
>      >
>      >         @Thomas: os::vm_page_size() is not used in
>      >         current_stack_region(), I think because of initialization
>      >         dependencies.
>      >
>      >
>      >     I don't see the dependency. It requires that it only be used after
>      >     os::init() has been called. AFAICS the first time we will use this
>      >     logic is when we attach the main thread, which happens after
>      >     os::init().
>      >
>      >     Thanks,
>      >     David
>      >
>      >         Best regards,
>      >         Gunter
>      >
>      >         From: Thomas Stüfe <thomas.stuefe at gmail.com
>      >         <mailto:thomas.stuefe at gmail.com>>
>      >         Date: Thursday, 17. August 2017 at 15:06
>      >         To: "Haug, Gunter" <gunter.haug at sap.com
>      >         <mailto:gunter.haug at sap.com>>
>      >         Cc: "hotspot-dev at openjdk.java.net
>      >         <mailto:hotspot-dev at openjdk.java.net>"
>      >         <hotspot-dev at openjdk.java.net <mailto:hotspot-dev at openjdk.java.net>>
>      >         Subject: Re: RFR(S): 8186286: [BSD] Primary thread's stack size
>      >         is reported incorrectly
>      >
>      >         Hi Gunter,
>      >
>      >
>      >         On Thu, Aug 17, 2017 at 2:24 PM, Haug, Gunter
>      >         <gunter.haug at sap.com
>      >         <mailto:gunter.haug at sap.com><mailto:gunter.haug at sap.com
>      >         <mailto:gunter.haug at sap.com>>> wrote:
>      >         Hi,
>      >
>      >         can I please have reviews and a sponsor fort the following small
>      >         bug fix:
>      >         http://cr.openjdk.java.net/~ghaug/webrevs/8186286/
>      >         <http://cr.openjdk.java.net/~ghaug/webrevs/8186286/>
>      >         https://bugs.openjdk.java.net/browse/JDK-8186286
>      >         <https://bugs.openjdk.java.net/browse/JDK-8186286>
>      >
>      >         At least on Mac OS 10.12 we have observed stack sizes of the
>      >         primary thread not aligned to pages boundries. This can be
>      >         provoked by e.g. setrlimit() (ulimit -s xxxx in the shell).This
>      >         voids the computation of the addresses of the guard pages.
>      >
>      >         Fix:
>      >         Apparently Mac OS actually rounds upwards to next multiple of
>      >         page size however, it is conservative to round downwards here to
>      >         be on the safe side.
>      >
>      >         Thanks and best regards,
>      >         Gunter
>      >
>      >         Thanks for the patch!
>      >
>      >         Very minor nits: what Alexey wrote (we also have "is_aligned").
>      >         Plus, any reason not to use os::vm_page_size()? Initialization
>      >         dependencies?
>      >
>      >         Kind Regards, Thomas
>      >
>      >
>      >
>      >
>      
>