RFR(S): 8199813: SIGSEGV in ThreadsList::includes()

[Gerald Thornbrugh]

Hi Dan,

Your changes look good to me.

Jerry


On 03/23/2018 02:55 PM, Daniel D. Daugherty wrote:
> Greetings,
>
> I have a small fix for a Thread-SMR bug:
>
> JDK-8199813 SIGSEGV in ThreadsList::includes()
> https://bugs.openjdk.java.net/browse/JDK-8199813
>
> Here's the webrev URL:
>
> http://cr.openjdk.java.net/~dcubed/8199813-webrev/0-for-jdk-hs/
>
> The failure mode for this bug is a SIGSEGV in ThreadsList::includes().
>
> The cause of this failure is use of a ThreadsListHandle by a JavaThread
> that is not yet on Threads list. This failure mode is intermittent since
> the ThreadsListHandle refers to a ThreadsList that may or may not get
> deleted by a racing thread. In particular, it has to get deleted in such
> a way that use of the ThreadsList causes a crash, e.g., page is freed.
>
> This fix has been tested on my Solaris-X64 server using my usual 24+
> hour Thread-SMR stress testing config. It has also been through Mach5
> hs-tier[1-5] testing. There have been no unexpected failures.
>
> This fix is currently going thru a Mach5 builds-tier1, jdk-tier[1-3],
> and hs-tier[1-3] run after resyncing; we don't want any new asserts()
> popping up in the jdk/jdk CI...
>
> Since this is a race fix, here are some details:
>
> As is usual for race fixes, there are more comments than code here.
>
> src/hotspot/share/runtime/thread.cpp
>     Use of a ThreadsListHandle by verify_not_published() before the
>     JavaThread is on the Thread list; this is the minimal fix for
>     the failure mode.
>
>     Save the shutdown thread in Threads::destroy_vm(). Also add a
>     comment explaining why IdealGraphPrinter::clean_up() is done
>     where it is.
>
> src/hotspot/os/linux/os_linux.cpp
>     Another use of a ThreadsListHandle before the JavaThread is on
>     the Threads list; found during testing of the fix by the new
>     assert() in the ThreadsListHandle ctr.
>
> src/hotspot/share/runtime/threadSMR.cpp
>     Add an assertion to the ThreadsListHandle ctr that catches
>     use of a ThreadsList that Threads::threads_do() won't be
>     able to protect.
>
>     Note: There is an exemption for the shutdown thread here.
>
> src/hotspot/share/runtime/vm_operations.hpp
>     Expose the shutdown thread so the new assert() in the
>     ThreadsListHandle ctr can do its job.
>
> src/hotspot/share/runtime/vm_operations.cpp
>     VM_Exit::_shutdown_thread should be volatile since it is
>     set by one thread and examined lock free by one or more
>     others.
>
>     The callers of VM_Exit::set_vm_exited() should set the
>     _shutdown_thread field since they have the earliest context.
>
>     Save the shutdown thread in VM_Exit::doit().
>
>
> Thanks, in advance, for any comments, suggestions, or feedback.
>
> Dan
>