8254877: GCLogPrecious::_lock rank constrains what locks you are allowed to have when crashing #900
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…wed to have when crashing
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👋 Welcome back eosterlund! A progress list of the required criteria for merging this PR into |
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| GCLogPreciousLine* head = _head; | ||
| GCLogPreciousLine* tail = _tail; | ||
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| if (head == NULL) { |
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I think this should be Atomic::load(&_head). This would make the head local variable unused.
| } | ||
| if (_tail != NULL) { | ||
| tail->set_next(line); | ||
| } |
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Either 61 should be using tail or 62 should be using _tail. If the latter then the tail local variable is unused.
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I had some offline discussions with StefanK. He would like to keep the stringStream that we have today, so that he can print the precious GC log from a debugger with less effort. He has an entirely different alternative. So I am going to close this PR, in favour of Stefan's solution. |
Today, when you crash, the GCLogPrecious::_lock is taken. This effectively limits you to only get clean crash reports if you crash or assert without holding a lock of rank tty or lower. It is arguably difficult to know what locks you are going to have when crashing. Therefore, I don't think the precious GC log should constrain possible crashing contexts in that fashion.
This patch inserts the precious GC lines into a linked list instead, that can be traversed concurrently, without holding any locks. This allows you to crash in contexts where "low" ranked locks are held.
I have manually verified that the hs_err precious GC log looks identical before and after my change.
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$ git fetch https://git.openjdk.java.net/jdk pull/900/head:pull/900$ git checkout pull/900