RFR: 8373096: JFR leak profiler: path-to-gc-roots search should be non-recursive [v2]

[Thomas Stuefe]

> A customer reported a crash when producing a JFR recording with `path-to-gc-roots=true`. It was a native stack overflow that occurred during the recursive path-to-gc-root search performed in the context of PathToGcRootsOperation.
> 
> We try to avoid this by limiting the maximum search depth (DFSClosure::max_dfs_depth). That solution is brittle, however, since recursion depth is not a good proxy for thread stack usage: it depends on many factors, e.g., compiler inlining decisions and platform specifics. In this case, the VMThread's stack was too small.
> 
> This RFE changes the algorithm to be non-recursive. 
> 
> Note that as a result of this change, the order in which oop maps are walked per oop is reversed : last oops are processed first. That should not matter for the end result, however. The search is still depth-first.
> 
> Note that after this patch, we could easily remove the max_depth limitation altogether. I left it in however since this was not the scope of this RFE.
> 
> Testing:
> 
> - Tested manually with very small (256K) thread stack size for the VMThread - the patched version works where the old version crashes out
> - Compared JFR recordings from both an unpatched version (with a large enough VMThread stack size) and a patched version; made sure that the content of "Old Object Sample" was identical
> - Ran locally all jtreg tests in jdk/jfr
> - GHAs

Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:

  fix

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28659/files
  - new: https://git.openjdk.org/jdk/pull/28659/files/5ac152db..e1a4736b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28659&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28659&range=00-01

  Stats: 16 lines in 2 files changed: 9 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/28659.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28659/head:pull/28659

PR: https://git.openjdk.org/jdk/pull/28659