HSX-24 Backport Code Review for memory commit failure fix (8013057)

[Daniel D. Daugherty]

Thanks for looking again!

Dan


On 6/10/13 9:43 AM, Zhengyu Gu wrote:
> Still good from NMT perspective.
>
> -Zhengyu
>
> On Jun 7, 2013, at 6:21 PM, Daniel D. Daugherty wrote:
>
>> Greetings,
>>
>> I have an HSX-24 backport of the proposed fix for the following bug:
>>
>>     8013057 assert(_needs_gc || SafepointSynchronize::is_at_safepoint())
>>             failed: only read at safepoint
>>
>> Here are the (round 0) webrev URLs for the HSX-24 backport:
>>
>> OpenJDK: http://cr.openjdk.java.net/~dcubed/8013057-webrev/0-hsx24/
>> Internal: http://javaweb.us.oracle.com/~ddaugher/8013057-webrev/0-hsx24/
>>
>> Here are the (round 3) webrev URLs for the HSX-25 version for reference:
>>
>> OpenJDK: http://cr.openjdk.java.net/~dcubed/8013057-webrev/3-hsx25/
>> Internal: http://javaweb.us.oracle.com/~ddaugher/8013057-webrev/3-hsx25/
>>
>> The easiest way to review the backport is to download and compare
>> the two patch files with your favorite file comparison tool:
>>
>> OpenJDK patch links:
>> http://cr.openjdk.java.net/~dcubed/8013057-webrev/0-hsx24/8013057_for_hsx24_exp.patch
>> http://cr.openjdk.java.net/~dcubed/8013057-webrev/3-hsx25/8013057_exp.patch
>>
>> Internal patch links:
>> http://javaweb.us.oracle.com/~ddaugher/8013057-webrev/0-hsx24/8013057_for_hsx24_exp.patch
>> http://javaweb.us.oracle.com/~ddaugher/8013057-webrev/3-hsx25/8013057_exp.patch
>>
>> For 'diff' oriented people (like me), here's my quick sanity of the two
>> patch files:
>>     - diff the patches
>>     - strip down to line additions and deletions
>>     - strip out the copyright changes
>>
>> $ diff 8013057-webrev/3-hsx25/8013057_exp.patch \
>>     8013057-webrev/0-hsx24/8013057_for_hsx24_exp.patch \
>>     | grep '^[<>] [+-] ' | grep -v Copyright
>> < +  return false;
>>> +  return false;
>> < +    vm_exit_out_of_memory(size, OOM_MMAP_ERROR, mesg);
>>> +    vm_exit_out_of_memory(size, mesg);
>> < +    vm_exit_out_of_memory(size, OOM_MMAP_ERROR, "committing reserved memory.");
>>> +    vm_exit_out_of_memory(size, "committing reserved memory.");
>> < +    vm_exit_out_of_memory(size, OOM_MMAP_ERROR, mesg);
>>> +    vm_exit_out_of_memory(size, mesg);
>> < +    vm_exit_out_of_memory(size, OOM_MMAP_ERROR, mesg);
>>> +    vm_exit_out_of_memory(size, mesg);
>> < +    vm_exit_out_of_memory(bytes, OOM_MMAP_ERROR, "committing reserved memory.");
>>> +    vm_exit_out_of_memory(bytes, "committing reserved memory.");
>> < +    vm_exit_out_of_memory(bytes, OOM_MMAP_ERROR, mesg);
>>> +    vm_exit_out_of_memory(bytes, mesg);
>> < +    vm_exit_out_of_memory(bytes, OOM_MMAP_ERROR, mesg);
>>> +    vm_exit_out_of_memory(bytes, mesg);
>> < +    vm_exit_out_of_memory(size, OOM_MMAP_ERROR, mesg);
>>> +    vm_exit_out_of_memory(size, mesg);
>> < -        vm_exit_out_of_memory(new_committed.byte_size(), OOM_MMAP_ERROR,
>>> -        vm_exit_out_of_memory(new_committed.byte_size(),
>> < -    vm_exit_out_of_memory(_size, OOM_MMAP_ERROR, "Allocator (commit)");
>>> -    vm_exit_out_of_memory(_size, "Allocator (commit)");
>> < -    vm_exit_out_of_memory(_page_size, OOM_MMAP_ERROR, "card table last card");
>>> -    vm_exit_out_of_memory(_page_size, "card table last card");
>> < -        vm_exit_out_of_memory(new_committed.byte_size(), OOM_MMAP_ERROR,
>>> -        vm_exit_out_of_memory(new_committed.byte_size(),
>> The majority of the diffs are due to new OOM failure type param that
>> was added in HSX-25 only. The "return false" shows up because HSX-24
>> has some left-over MacOS X port cruft that someone removed in HSX-25
>> so the "return false" looks like it was added in different places.
>>
>> The remainder is the HSX-25 round 3 code review invite with the
>> code blocks updated for HSX-24.
>>
>>
>> Testing:
>> - Aurora Adhoc vm.quick batch for all OSes in the following configs:
>>   {Client VM, Server VM} x {fastdebug} x {-Xmixed}
>> - I've created a standalone Java stress test with a shell script
>>   wrapper that reproduces the failing code paths on my Solaris X86
>>   server and on Ron's DevOps Linux machine. This test will not be
>>   integrated since running the machine out of swap space is very
>>   disruptive (crashes the window system, causes various services to
>>   exit, etc.)
>>
>> There are three parts to this fix:
>>
>> 1) Detect commit memory failures on Linux and Solaris where the
>>    previous reservation can be lost and call vm_exit_out_of_memory()
>>    to report the resource exhaustion. Add os::commit_memory_or_exit()
>>    API to provide more consistent handling of vm_exit_out_of_memory()
>>    calls.
>> 2) Change existing os::commit_memory() calls to make the executable
>>    status of memory more clear; this makes security analysis easier.
>> 3) Clean up some platform dependent layer calls that were resulting
>>    in extra NMT accounting. Clean up some mmap() return value checks.
>>
>> Gory details are below. As always, comments, questions and
>> suggestions are welome.
>>
>> Dan
>>
>>
>> Gory Details:
>>
>> The VirtualSpace data structure is built on top of the ReservedSpace
>> data structure. VirtualSpace presumes that failed os::commit_memory()
>> calls do not affect the underlying ReservedSpace memory mappings.
>> That assumption is true on MacOS X and Windows, but it is not true
>> on Linux or Solaris. The mmap() system call on Linux or Solaris can
>> lose previous mappings in the event of certain errors. On MacOS X,
>> the mmap() system call clearly states that previous mappings are
>> replaced only on success. On Windows, a different set of APIs are
>> used and they do not document any loss of previous mappings.
>>
>> The solution is to implement the proper failure checks in the
>> os::commit_memory() implementations on Linux and Solaris. On MacOS X
>> and Windows, no additional checks are needed.
>>
>> During code review round 1, there was a request from the GC team to
>> provide an os::commit_memory_or_exit() entry point in order to preserve
>> the existing error messages on all platforms. This entry point allows
>> code like this:
>>
>> src/share/vm/gc_implementation/parallelScavenge/cardTableExtension.cpp:
>>
>> 652       if (!os::commit_memory((char*)new_committed.start(),
>> 653                              new_committed.byte_size())) {
>> 654         vm_exit_out_of_memory(new_committed.byte_size(),
>> 655                               "card table expansion");
>>
>> to be replaced with code like this:
>>
>> 652       os::commit_memory_or_exit((char*)new_committed.start(),
>> 653                                 new_committed.byte_size(), !ExecMem,
>> 654                                 "card table expansion");
>>
>> All uses of os::commit_memory() have been visited and those locations
>> that previously exited on error have been updated to use the new entry
>> point. This new entry point cleans up the original call sites and the
>> vm_exit_out_of_memory() calls are now consistent on all platforms.
>>
>> As a secondary change, while visiting all os::commit_memory() calls, I
>> also updated them to use the new ExecMem enum in order to make the
>> executable status of the memory more clear. Since executable memory can
>> be an attack vector, it is prudent to make the executable status of
>> memory crystal clear. This also allowed me to remove the default
>> executable flag value of 'false'. Now all new uses of commit_memory()
>> must be clear about the executable status of the memory.
>>
>> There are also tertiary changes where some of the pd_commit_memory()
>> calls were calling os::commit_memory() instead of calling their sibling
>> os::pd_commit_memory(). This resulted in double NMT tracking so this
>> has also been fixed. There were also some incorrect mmap)() return
>> value checks which have been fixed.
>>
>> Just to be clear: This fix simply properly detects the "out of swap
>> space" condition on Linux and Solaris and causes the VM to fail in a
>> more orderly fashion with a message that looks like this:
>>
>> The Java process' stderr will show:
>>
>> INFO: os::commit_memory(0xfffffd7fb2522000, 4096, 4096, 0) failed; errno=11
>> #
>> # There is insufficient memory for the Java Runtime Environment to continue.
>> # Native memory allocation (mmap) failed to map 4096 bytes for committing reserved memory.
>> # An error report file with more information is saved as:
>> # /work/shared/bugs/8013057/looper.03/hs_err_pid9111.log
>>
>> The hs_err_pid file will have the more verbose info:
>>
>> #
>> # There is insufficient memory for the Java Runtime Environment to continue.
>> # Native memory allocation (mmap) failed to map 4096 bytes for committing reserved memory.
>> # Possible reasons:
>> #   The system is out of physical RAM or swap space
>> #   In 32 bit mode, the process size limit was hit
>> # Possible solutions:
>> #   Reduce memory load on the system
>> #   Increase physical memory or swap space
>> #   Check if swap backing store is full
>> #   Use 64 bit Java on a 64 bit OS
>> #   Decrease Java heap size (-Xmx/-Xms)
>> #   Decrease number of Java threads
>> #   Decrease Java thread stack sizes (-Xss)
>> #   Set larger code cache with -XX:ReservedCodeCacheSize=
>> # This output file may be truncated or incomplete.
>> #
>> #  Out of Memory Error (/work/shared/bug_hunt/hsx_rt_latest/exp_8013057/src/os/solaris/vm/os_solaris.cpp:2791), pid=9111, tid=21
>> #
>> # JRE version: Java(TM) SE Runtime Environment (8.0-b89) (build 1.8.0-ea-b89)
>> # Java VM: Java HotSpot(TM) 64-Bit Server VM (25.0-b33-bh_hsx_rt_exp_8013057_dcubed-product-fastdebug mixed mode solaris-amd64 compressed oops)
>> # Core dump written. Default location: /work/shared/bugs/8013057/looper.03/core or core.9111
>> #
>>
>> You might be wondering why we are assuming that the failed mmap()
>> commit operation has lost the 'reserved memory' mapping.
>>
>>     We have no good way to determine if the 'reserved memory' mapping
>>     is lost. Since all the other threads are not idle, it is possible
>>     for another thread to have 'reserved' the same memory space for a
>>     different data structure. Our thread could observe that the memory
>>     is still 'reserved' but we have no way to know that the reservation
>>     isn't ours.
>>
>> You might be wondering why we can't recover from this transient
>> resource availability issue.
>>
>>     We could retry the failed mmap() commit operation, but we would
>>     again run into the issue that we no longer know which data
>>     structure 'owns' the 'reserved' memory mapping. In particular, the
>>     memory could be reserved by native code calling mmap() directly so
>>     the VM really has no way to recover from this failure.
>>
>> You might be wondering why part of this work is deferred:
>>
>> 2749     if (!recoverable_mmap_error(err)) {
>> 2750       // However, it is not clear that this loss of our reserved mapping
>> 2751       // happens with large pages on Linux or that we cannot recover
>> 2752       // from the loss. For now, we just issue a warning and we don't
>> 2753       // call vm_exit_out_of_memory(). This issue is being tracked by
>> 2754       // JBS-8007074.
>> 2755       warn_fail_commit_memory(addr, size, alignment_hint, exec, err);
>> 2756 //    vm_exit_out_of_memory(size, "committing reserved memory.");
>> 2757     }
>> 2758     // Fall through and try to use small pages
>>
>>     When line 2756 is enabled and UseHugeTLBFS is specified, then the
>>     VM will exit because no more huge/large pages are available. It is
>>     not yet clear that this transition from large to small pages is
>>     actually unsafe, but we don't yet have proof that it is safe
>>     either. More research will be done via JBS-8007074.
>>
>> If you've made it this far without falling asleep or drooling on your
>> keyboard, I applaud you!