RFR: 8189170: Add option to disable stack overflow checking in primordial thread for use with JNI_CreateJavaJVM

[Thomas Stüfe]

On Fri, Nov 17, 2017 at 4:40 PM, Daniel D. Daugherty <
daniel.daugherty at oracle.com> wrote:

> On 11/14/17 5:39 AM, David Holmes wrote:
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8189170
>
> webrev: http://cr.openjdk.java.net/~dholmes/8189170/webrev/
>
>
> src/hotspot/os/aix/os_aix.cpp
>     No comments.
>
> src/hotspot/os/aix/os_aix.hpp
>     No comments.
>
> src/hotspot/os/bsd/os_bsd.cpp
>     L880: // thread in any special way - so just report 'false'
>         Nit - needs a period after 'false' to make it a sentence.
>
>     L882:     return false;
>         Nit - indent should be 2 spaces.
>
> src/hotspot/os/bsd/os_bsd.hpp
>     No comments.
>
> src/hotspot/os/linux/os_linux.cpp
>     L947:   if (stack_size >= (size_t)(3 * page_size()))
>         Nit - needs '{' and '}' on the if-statement body.
>
>     L3070: // always place it right after end of the mapped region
>         Nit - needs a period after 'region' to make it a sentence.
>         (Not your problem, but you did update the sentence...)
>
> src/hotspot/os/linux/os_linux.hpp
>     No comments.
>
> src/hotspot/os/solaris/os_solaris.cpp
>     No comments other than I learned something new about thr_main() :-)
>     Thanks for cleaning up that mess.
>
> src/hotspot/os/windows/os_windows.cpp
>     L452: // thread in any special way - so just report 'false'
>         Nit - needs a period after 'false' to make it a sentence.
>
>     L454:     return false;
>         Nit - indent should be 2 spaces.
>
> src/hotspot/share/gc/shared/threadLocalAllocBuffer.cpp
>     No comments.
>
> src/hotspot/share/runtime/globals.hpp
>     L1181:   experimental(bool, DisablePrimordialThreadGuardPages, false,
>         Experimental or diagnostic?
>
> src/hotspot/share/runtime/os.hpp
>     L450:   // that loads/creates the JVM via JNI_CreateJavaVM
>         Nit - needs a period after 'JNI_CreateJavaVM'.
>
>     L453:   // launcher nevers uses the primordial thread as the main
> thread, but
>         Typo - 'nevers' -> 'never'
>
>     L455:   // have to special-case handling of the primordial thread if
> it attaches
>         Typo - 'have to' -> 'have'
>
> src/hotspot/share/runtime/thread.cpp
>     I like the new log message.
>
> src/hotspot/share/runtime/thread.inline.hpp
>     L159:   if (os::uses_stack_guard_pages() &&
>     L160:       !(DisablePrimordialThreadGuardPages &&
> os::is_primordial_thread())) {
>         I'm not sure why, but I had to read these two lines several
>         times before I convinced myself the logic is right.
>
> I'm good with the code changes. Your call on whether to fix the
> bits or not.
>
> Regarding this part of Thomas' review:
>
> Or, something like this:
> static bool is_primordial_thread(void) WINDOWS_ONLY({return false;})
> BSD_ONLY({return false;})
>
>
> I can do that. I'll see if anyone else has any comments on this.
>
>
> I'm assuming that Thomas means for the above to be at the
> platform independent layer (runtime/os.hpp?) so it is more
> obvious to the reader that the function doesn't do anything
> on those two platforms... I know we dislike such things at
> the platform independent layer, but it does feel appropriate
> to make this limitation more obvious.
>
> I would be okay if you made the change that Thomas is suggesting.
>
> Thumbs up!
>
> Dan
>
>
>
>
> There are three parts to this which made it somewhat more complicated than
> I had envisaged:
>
> 1. Add the flag and disable the guards.
>
> This is relatively straight-forward:
>
>  void JavaThread::create_stack_guard_pages() {
>    if (!os::uses_stack_guard_pages() ||
>        _stack_guard_state != stack_guard_unused ||
>        (DisablePrimordialThreadGuardPages && os::is_primordial_thread()))
> {
>        log_info(os, thread)("Stack guard page creation for thread "
>                             UINTX_FORMAT " disabled",
> os::current_thread_id());
>      return;
>
> with a tweak in JavaThread::stack_guards_enabled as well.
>
> 2. Promote os::XXX::is_initial_thread to os::is_primordial_thread()
>
> We have three platforms that already implement this functionality: Linux,
> Solaris and AIX. For BSD/OSX and Windows we don't attempt to do anything
> different for the primordial thread, and we don't have a way to detect the
> primordial thread - so is_primordial_thread() just returns false.
>
> I also tidied up some comments regarding terminology.
>
> 3. Thomas noticed that we unconditionally subtract 2*page_size() from the
> rlimit stack size, without checking it was bigger than 2*page_size() to
> start with. I was unsure how to tackle this. It's no good leaving
> stack_size at zero so I opted to ensure we would have at least one page
> left. Of course in such cases we would hit the bug in libc (if it still
> exists, which seems unlikely but time consuming to establish).
>
> Testing:
>   - Tier 1 (JPRT) testing with a modified launcher that uses the
> primordial thread
>     - with guard pages enabled
>     - with guard pages disabled
>   - Tier 1 (JPRT) normal JDK build (which should be unaffected by this
> change)
>
> The testing was primarily to ensure that disabling the stack guards on the
> primordial thread wasn't totally broken. A number of tests fail:
> - setting -Xss32m fails for the primordial thread when guards are enabled
> and the rlimit is 8m
> - tests that would hit StackOverflowError crash the VM when guards are
> disabled (as you would expect).
> - runtime/execstack/Testexecstack.java crashes when the guards are
> disabled
>
> Thanks,
> David
>
>
>