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8261354: SIGSEGV at MethodIteratorHost #4143

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@jbachorik jbachorik commented May 21, 2021

The MethodIteratorHost will iterate over previous versions of redefined classes but the number of methods in that class is retrieved only for the current version.
Since the previous versions may theoretically, and before JDK 15 also practically, contain fewer methods than the current version (hotspot did support adding private static methods during retransformation) this can lead to SIGSEGV when the iterator tries accessing out-of-range method element.

Although for after JDK 15 it is not possible to have differing number of methods between multiple versions of a retransformed class it feels right not to rely on the implementation detail and re-retrieve the number of methods per each class version.

All jdk_jfr tests are passing on Linux x64 and MacOS x64


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@bridgekeeper bridgekeeper bot commented May 21, 2021

👋 Welcome back jbachorik! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

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@openjdk openjdk bot commented May 21, 2021

@jbachorik The following label will be automatically applied to this pull request:

  • hotspot-jfr

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

@openjdk openjdk bot added the hotspot-jfr label May 21, 2021
@jbachorik jbachorik changed the title 8203359: SIGSEGV at MethodIteratorHost 8261354: SIGSEGV at MethodIteratorHost May 21, 2021
@jbachorik jbachorik marked this pull request as ready for review May 21, 2021
@openjdk openjdk bot added the rfr label May 21, 2021
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@mlbridge mlbridge bot commented May 21, 2021

Webrevs

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@mgronlun mgronlun left a comment

Wow, this was subtle - great work in locating the root cause Jaroslav!

Were you able to reproduce this issue?

I wonder how this affects the Filter construct that is intended to prevent multiple entries from being serialized (and to leave when done). Now it looks like there is no state carried between iterations, unfortunately. This might be ok in practice, it would probably be ok to have multiple entries of the same method serialized (although redundant). Might need to reconsider if the Filter should still be used here.

Looks good, thank you
Markus

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@openjdk openjdk bot commented May 21, 2021

@jbachorik This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8261354: SIGSEGV at MethodIteratorHost

Reviewed-by: mgronlun

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At the time when this comment was updated there had been 11 new commits pushed to the master branch:

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@openjdk openjdk bot added the ready label May 21, 2021
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@mgronlun mgronlun commented May 21, 2021

/reviewer remove mgronlun

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@openjdk openjdk bot commented May 21, 2021

@mgronlun Only the author (@jbachorik) is allowed to issue the reviewer command.

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@jbachorik jbachorik commented May 21, 2021

Were you able to reproduce this issue?

Well, yes. But I did it with BTrace script - the reproducer requires an instrumenting agent which is adding private static methods and since BTrace is already doing that for JDK 11 it was the quickest way to bisect :)

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@jbachorik jbachorik commented May 21, 2021

/reviewer remove mgronlun

@mgronlun Do you want to 'unreview' this PR?

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@mgronlun mgronlun commented May 21, 2021

Hi again,

I noticed the Filter stuff after I clicked Approve, and it was an attempt to roll back my approve state - I don't know if it is possible to even do that. So consider it approved, but we need to think about how to handle the Filter thing. Because now it will no longer work as intended, so maybe consider removing it.

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@jbachorik jbachorik commented May 21, 2021

I can remove the filter before integrating to make the code less confusing - since the filter has no function right now it would be better if it is not there at all.

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@jbachorik jbachorik commented May 22, 2021

/integrate

@openjdk openjdk bot closed this May 22, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels May 22, 2021
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@openjdk openjdk bot commented May 22, 2021

@jbachorik Since your change was applied there have been 13 commits pushed to the master branch:

Your commit was automatically rebased without conflicts.

Pushed as commit 2462316.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

@jbachorik jbachorik deleted the jb/8261354 branch May 22, 2021
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