review (S) for 6975006: assert(check.is_deoptimized_frame()) failed: missed deopt

[Vladimir Kozlov]

Looks good.

Vladimir

Tom Rodriguez wrote:
> http://cr.openjdk.java.net/~never/6975006
> 
> 6975006: assert(check.is_deoptimized_frame()) failed: missed deopt
> Reviewed-by:
> 
> The safepointing logic treats threads that are thread_in_native as if
> they are halted since the Java state is safe while we are in native
> state.  If the thread happens to return from native during the
> safepoint it will simply come to a halt.  On sparc this creates some
> complexity when patching for deoptimization because the return address
> is kept in a register and only flushed to stack by the chip.  We force
> flushing of the windows in the JNI stub but because of the way
> register windows work this doesn't help the frame that is just above a
> native wrapper since the window might be on chip while the native
> wrapper itself is executing.  There's machinery in the deopt code that
> detects the case where the caller of a native wrapper is the one being
> deoptimized and arranges for the native wrapper to rewrite the return
> address when it comes out of native.  The problem is that this code
> examines the current state of the thread at the time the deopt occurs
> not what state was when the safepoint started.  This creates a little
> race where a native wrapper might come to a halt on it's own after the
> safepoint started but before the deopt patching occurred, which
> sidesteps the deopt suspend logic because it's not in one of the
> thread_in_native states.  The fix is to record the state of the thread
> at the beginning of the safepoint and consult that when triggering the
> deopt suspend logic.
> 
> Tested by repeatedly running test with -XX:+DeoptimizeALot.
> Previously it would fail within 5 minutes but after the fix it ran
> overnight until I simply killed it.