Array accesses using sun.misc.Unsafe cause data corruption or SIGSEGV
John Rose
john.r.rose at oracle.com
Fri Jul 17 19:31:04 UTC 2015
Thanks Serkan and Martijn for reporting and analyzing this.
We had a very similar bug reported internally, and we just integrated a fix:
http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/rev/3816de51b5e7
Would you mind checking if it fixes your problem also?
Best wishes,
— John
On Jul 12, 2015, at 5:07 AM, Serkan Özal <serkan at hazelcast.com> wrote:
>
> Hi Martjin,
>
> Thanks for your interest and comment for making this thread a little bit more hot.
>
>
> From my previous message (http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-June/018221.html <http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-June/018221.html>):
>
> I added some additional logs to "vm/c1/c1_Canonicalizer.cpp":
>
>
> void Canonicalizer::do_UnsafeGetRaw(UnsafeGetRaw* x) {
> if (OptimizeUnsafes) do_UnsafeRawOp(x);
> tty->print_cr("Canonicalizer: do_UnsafeGetRaw id %d: base = id %d, index = id %d, log2_scale = %d",
> x->id(), x->base()->id(), x->index()->id(), x->log2_scale());
> }
>
>
> void Canonicalizer::do_UnsafePutRaw(UnsafePutRaw* x) {
> if (OptimizeUnsafes) do_UnsafeRawOp(x);
> tty->print_cr("Canonicalizer: do_UnsafePutRaw id %d: base = id %d, index = id %d, log2_scale = %d",
> x->id(), x->base()->id(), x->index()->id(), x->log2_scale());
> }
>
>
>
> So I run the test by calculating address as:
> - "int * long" (int is index and long is 8l)
> - "long * long" (the first long is index and the second long is 8l)
> - "int * int" (the first int is index and the second int is 8)
>
> Here are the logs:
>
>
> int * long:
>
> Canonicalizer: do_UnsafeGetRaw id 18: base = id 16, index = id 17, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 20: base = id 16, index = id 19, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 16, index = id 21, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 24: base = id 16, index = id 23, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 33: base = id 13, index = id 27, log2_scale = 3
> Canonicalizer: do_UnsafeGetRaw id 36: base = id 13, index = id 27, log2_scale = 3
>
> long * long:
>
> Canonicalizer: do_UnsafeGetRaw id 18: base = id 16, index = id 17, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 20: base = id 16, index = id 19, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 16, index = id 21, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 24: base = id 16, index = id 23, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 35: base = id 13, index = id 14, log2_scale = 3
> Canonicalizer: do_UnsafeGetRaw id 37: base = id 13, index = id 14, log2_scale = 3
>
> int * int:
>
> Canonicalizer: do_UnsafeGetRaw id 18: base = id 16, index = id 17, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 20: base = id 16, index = id 19, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 16, index = id 21, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 24: base = id 16, index = id 23, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 33: base = id 13, index = id 29, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 36: base = id 13, index = id 29, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 19: base = id 8, index = id 15, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 8, index = id 15, log2_scale = 0
>
> As you can see, at the problematic runs ("int * long" and "long * long") there are two scaling.
> One for "Unsafe.put" and the other one is for "Unsafe.get" and these instructions points to
> same "base" and "index" instructions. This means that address is scaled one more time because there should be only one scale.
>
>
> With this fix (or attempt since I am not %100 sure if it is perfect/optimum way or not), I prevent multiple scaling on the same index instruction.
>
> Also one of my previous messages (http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-July/018383.html <http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-July/018383.html>) shows that there are multiple scaling on the index so when it scaled multiple, anymore it shows somewhere or anywhere in the memory.
>
> On Sun, Jul 12, 2015 at 2:54 PM, Martijn Verburg <martijnverburg at gmail.com <mailto:martijnverburg at gmail.com>> wrote:
> Non reviewer here, but I'd add to the comment *why* you don't want to scale again.
>
> Cheers,
> Martijn
>
> On 12 July 2015 at 11:29, Serkan Özal <serkan at hazelcast.com <mailto:serkan at hazelcast.com>> wrote:
> Hi all,
>
> I have created a webrev for review including the patch and shared for public access from here: https://s3.amazonaws.com/jdk-8087134/webrev.00/index.html <https://s3.amazonaws.com/jdk-8087134/webrev.00/index.html>
>
> Regards.
>
> On Sat, Jul 4, 2015 at 9:06 PM, Serkan Özal <serkan at hazelcast.com <mailto:serkan at hazelcast.com>> wrote:
> Hi,
>
> I have added some logs to show that problem is caused by double scaling of offset (index)
>
> Here is my updated (log messages added) reproducer code:
>
>
> int count = 100000;
> long size = count * 8L;
> long baseAddress = unsafe.allocateMemory(size);
> System.out.println("Start address: " + Long.toHexString(baseAddress) +
> ", End address: " + Long.toHexString(baseAddress + size));
>
> for (int i = 0; i < count; i++) {
> long address = baseAddress + (i * 8L);
> System.out.println(
> "Normal: " + Long.toHexString(address) + ", " +
> "If double scaled: " + Long.toHexString(baseAddress + (i * 8L * 8L)));
> long expected = i;
> unsafe.putLong(address, expected);
> unsafe.getLong(address);
> }
>
>
> After sometime it crashes as
>
>
> ...
> Current thread (0x0000000002068800): JavaThread "main" [_thread_in_Java, id=10412, stack(0x00000000023f0000,0x00000000024f0000)]
>
> siginfo: ExceptionCode=0xc0000005, reading address 0x0000000059061020
> ...
> ...
>
>
> And here is output of the execution until crash:
>
> Start address: 58bbcfa0, End address: 58c804a0
> Normal: 58bbcfa0, If double scaled: 58bbcfa0
> Normal: 58bbcfa8, If double scaled: 58bbcfe0
> Normal: 58bbcfb0, If double scaled: 58bbd020
> ...
> ...
> Normal: 58c517b0, If double scaled: 59061020
>
>
> As seen from the logs and crash dump, double scaled version of target address (If double scaled: 59061020) is the same with the problematic address (siginfo: ExceptionCode=0xc0000005, reading address 0x0000000059061020) that causes to crash while accessing it.
>
> So I think, it is obvious that the crash is caused by wrong optimization of index value since index is scaled two times (for Unsafe::put and Unsafe::get) instead of only one time. Then double scaled index points to invalid memory address.
>
> Regards.
>
> On Sun, Jun 14, 2015 at 2:39 PM, Serkan Özal <serkan at hazelcast.com <mailto:serkan at hazelcast.com>> wrote:
> Hi all,
>
> I had dived into the issue with JDK-HotSpot commits and
> the issue arised after this commit: http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/rev/a60a1309a03a <http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/rev/a60a1309a03a>
>
> Then I added some additional logs to "vm/c1/c1_Canonicalizer.cpp":
>
> void Canonicalizer::do_UnsafeGetRaw(UnsafeGetRaw* x) {
> if (OptimizeUnsafes) do_UnsafeRawOp(x);
> tty->print_cr("Canonicalizer: do_UnsafeGetRaw id %d: base = id %d, index = id %d, log2_scale = %d",
> x->id(), x->base()->id(), x->index()->id(), x->log2_scale());
> }
>
> void Canonicalizer::do_UnsafePutRaw(UnsafePutRaw* x) {
> if (OptimizeUnsafes) do_UnsafeRawOp(x);
> tty->print_cr("Canonicalizer: do_UnsafePutRaw id %d: base = id %d, index = id %d, log2_scale = %d",
> x->id(), x->base()->id(), x->index()->id(), x->log2_scale());
> }
>
>
>
> So I run the test by calculating address as
> - "int * long" (int is index and long is 8l)
> - "long * long" (the first long is index and the second long is 8l)
> - "int * int" (the first int is index and the second int is 8)
>
> Here are the logs:
>
> int * long:
> Canonicalizer: do_UnsafeGetRaw id 18: base = id 16, index = id 17, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 20: base = id 16, index = id 19, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 16, index = id 21, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 24: base = id 16, index = id 23, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 33: base = id 13, index = id 27, log2_scale = 3
> Canonicalizer: do_UnsafeGetRaw id 36: base = id 13, index = id 27, log2_scale = 3
>
> long * long:
> Canonicalizer: do_UnsafeGetRaw id 18: base = id 16, index = id 17, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 20: base = id 16, index = id 19, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 16, index = id 21, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 24: base = id 16, index = id 23, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 35: base = id 13, index = id 14, log2_scale = 3
> Canonicalizer: do_UnsafeGetRaw id 37: base = id 13, index = id 14, log2_scale = 3
>
> int * int:
> Canonicalizer: do_UnsafeGetRaw id 18: base = id 16, index = id 17, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 20: base = id 16, index = id 19, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 16, index = id 21, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 24: base = id 16, index = id 23, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 33: base = id 13, index = id 29, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 36: base = id 13, index = id 29, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 19: base = id 8, index = id 15, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 8, index = id 15, log2_scale = 0
>
> As you can see, at the problematic runs ("int * long" and "long * long") there are two scaling.
> One for "Unsafe.put" and the other one is for "Unsafe.get" and these instructions points to
> same "base" and "index" instructions.
> This means that address is scaled one more time because there should be only one scale.
>
>
>
> When I debugged the non-problematic run ("int * int"),
> I saw that "instr->as_ArithmeticOp();" is always returns "null" then "match_index_and_scale" method returns "false" always.
> So there is no scaling.
>
> static bool match_index_and_scale(Instruction* instr,
> Instruction** index,
> int* log2_scale) {
> ...
>
> ArithmeticOp* arith = instr->as_ArithmeticOp();
> if (arith != NULL) {
> ...
> }
>
> return false;
> }
>
>
>
> Then I have added my fix attempt to prevent multiple scaling for Unsafe instructions points to same index instruction like this:
>
> void Canonicalizer::do_UnsafeRawOp(UnsafeRawOp* x) {
> Instruction* base = NULL;
> Instruction* index = NULL;
> int log2_scale;
>
> if (match(x, &base, &index, &log2_scale)) {
> x->set_base(base);
> x->set_index(index);
> // The fix attempt here
> // /////////////////////////////
> if (index != NULL) {
> if (index->is_pinned()) {
> log2_scale = 0;
> } else {
> if (log2_scale != 0) {
> index->pin();
> }
> }
> }
> // /////////////////////////////
> x->set_log2_scale(log2_scale);
> if (PrintUnsafeOptimization) {
> tty->print_cr("Canonicalizer: UnsafeRawOp id %d: base = id %d, index = id %d, log2_scale = %d",
> x->id(), x->base()->id(), x->index()->id(), x->log2_scale());
> }
> }
> }
>
> In this fix attempt, if there is a scaling for the Unsafe instruction, I pin index instruction of that instruction
> and at next calls, if the index instruction is pinned, I assummed that there is already scaling so no need to another scaling.
>
> After this fix, I rerun the problematic test ("int * long") and it works with these logs:
>
> int * long (after fix):
> Canonicalizer: do_UnsafeGetRaw id 18: base = id 16, index = id 17, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 20: base = id 16, index = id 19, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 22: base = id 16, index = id 21, log2_scale = 0
> Canonicalizer: do_UnsafeGetRaw id 24: base = id 16, index = id 23, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 35: base = id 13, index = id 14, log2_scale = 3
> Canonicalizer: do_UnsafeGetRaw id 37: base = id 13, index = id 14, log2_scale = 0
> Canonicalizer: do_UnsafePutRaw id 21: base = id 8, index = id 11, log2_scale = 3
> Canonicalizer: do_UnsafeGetRaw id 23: base = id 8, index = id 11, log2_scale = 0
>
> I am not sure my fix attempt is a really fix or maybe there are better fixes.
>
> Regards.
>
> --
>
> Serkan ÖZAL
>
> Btw, (thanks to one my colleagues), when address calculation in the loop is
> converted to
> long address = baseAddress + (i * 8)
> test passes. Only difference is next long pointer is calculated using
> integer 8 instead of long 8.
> ```
> for (int i = 0; i < count; i++) {
> long address = baseAddress + (i * 8); // <--- here, integer 8 instead
> of long 8
> long expected = i;
> unsafe.putLong(address, expected);
> long actual = unsafe.getLong(address);
> if (expected != actual) {
> throw new AssertionError("Expected: " + expected + ", Actual: " +
> actual);
> }
> }
> ```
> On Tue, Jun 9, 2015 at 1:07 PM Mehmet Dogan <mehmet at hazelcast.com <http://mail.openjdk.java.net/mailman/listinfo/hotspot-compiler-dev>> wrote:
> > Hi all,
> >
> > While I was testing my app using java 8, I encountered the previously
> > reported sun.misc.Unsafe issue.
> >
> > https://bugs.openjdk.java.net/browse/JDK-8076445 <https://bugs.openjdk.java.net/browse/JDK-8076445>
> >
> > http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-April/017685.html <http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-April/017685.html>
> >
> > Issue status says it's resolved with resolution "Cannot Reproduce". But
> > unfortunately it's still reproducible using "1.8.0_60-ea-b18" and
> > "1.9.0-ea-b67".
> >
> > Test is very simple:
> >
> > ```
> > public static void main(String[] args) throws Exception {
> > Unsafe unsafe = findUnsafe();
> > // 10000 pass
> > // 100000 jvm crash
> > // 1000000 fail
> > int count = 100000;
> > long size = count * 8L;
> > long baseAddress = unsafe.allocateMemory(size);
> >
> > try {
> > for (int i = 0; i < count; i++) {
> > long address = baseAddress + (i * 8L);
> >
> > long expected = i;
> > unsafe.putLong(address, expected);
> >
> > long actual = unsafe.getLong(address);
> >
> > if (expected != actual) {
> > throw new AssertionError("Expected: " + expected + ",
> > Actual: " + actual);
> > }
> > }
> > } finally {
> > unsafe.freeMemory(baseAddress);
> > }
> > }
> > ```
> > It's not failing up to version 1.8.0.31, by starting 1.8.0.40 test is
> > failing constantly.
> >
> > - With iteration count 10000, test is passing.
> > - With iteration count 100000, jvm is crashing with SIGSEGV.
> > - With iteration count 1000000, test is failing with AssertionError.
> >
> > When one of compilation (-Xint) or inlining (-XX:-Inline) or
> > on-stack-replacement (-XX:-UseOnStackReplacement) is disabled, test is not
> > failing at all.
> >
> > I tested on platforms:
> > - Centos-7/openjdk-1.8.0.45
> > - OSX/oraclejdk-1.8.0.40
> > - OSX/oraclejdk-1.8.0.45
> > - OSX/oraclejdk-1.8.0_60-ea-b18
> > - OSX/oraclejdk-1.9.0-ea-b67
> >
> > Previous issue comment (
> > https://bugs.openjdk.java.net/browse/JDK-8076445?focusedCommentId=13633043#comment-13633043 <https://bugs.openjdk.java.net/browse/JDK-8076445?focusedCommentId=13633043#comment-13633043>)
> > says "Cannot reproduce based on the latest version". I hope that latest
> > version is not mentioning to '1.8.0_60-ea-b18' or '1.9.0-ea-b67'. Because
> > both are failing.
> >
> > I'm looking forward to hearing from you.
> >
> > Thanks,
> > -Mehmet Dogan-
> > --
> >
> > @mmdogan
> >
>
> --
> Serkan ÖZAL
> Remotest Software Engineer
> GSM: +90 542 680 39 18 <tel:%2B90%20542%20680%2039%2018>
> Twitter: @serkan_ozal
>
>
>
> --
> Serkan ÖZAL
> Remotest Software Engineer
> GSM: +90 542 680 39 18 <tel:%2B90%20542%20680%2039%2018>
> Twitter: @serkan_ozal
>
>
>
> --
> Serkan ÖZAL
> Remotest Software Engineer
> GSM: +90 542 680 39 18 <tel:%2B90%20542%20680%2039%2018>
> Twitter: @serkan_ozal
>
>
>
>
> --
> Serkan ÖZAL
> Remotest Software Engineer
> GSM: +90 542 680 39 18
> Twitter: @serkan_ozal
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