RFR: JDK-8277056: Combining several C2 Print* flags asserts in xmlStream::pop_tag [v2]

[Xin Liu]

On Thu, 21 Apr 2022 08:08:15 GMT, Tobias Holenstein <duke at openjdk.java.net> wrote:

>> Sometimes the writing to xmlStream is mixed from several threads, and therefore the `xmlStream` tag stack can end up in a bad state. When this occurs, the VM crashes in `xmlStream::pop_tag` with `assert(false) failed: bad tag in log`.
>> 
>> The logging between `xtty->head` and `xtty->tail` is guarded by a ttyLocker which also locks `VMThread::should_terminate()` (ttyLocker is needed here to serializes the output info about the termination of the VMThread). 
>> 
>> The problem is that `print_metadata` and `dump_asm` may block for safepoint which then releases the ttyLocker (`break_tty_lock_for_safepoint`). When the `print_metadata` or `dump_asm` continues after the safepoint other threads could have taken the ttyLocker and may be busy printing and interfere with the tag stack of `xmlStream`.
>> 
>> The solution is to call `print_metadata` and `dump_asm` first and let them write to a local stringStream. Then acquire the ttyLocker to do the printing (using the local stringStream) and use a separate ttyLocker for `VMThread::should_terminate()`
>> 
>> The same issue was already targeted in https://bugs.openjdk.java.net/browse/JDK-8153527 but the fix was incomplete.
>
> Tobias Holenstein has updated the pull request incrementally with one additional commit since the last revision:
> 
>   changed print to print_raw

LGTM.  I am not a reviewer.

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Marked as reviewed by xliu (Committer).

PR: https://git.openjdk.java.net/jdk/pull/8203