RFR: 8214315: G1: fatal error: acquiring lock SATB_Q_FL_lock/1 out of order with lock tty_lock/0

[Thomas Schatzl]

Hi,

On Fri, 2018-12-07 at 01:31 -0500, Kim Barrett wrote:
> Please review this change to the lock rank for the tty_lock.  We
> introduce a new lock rank 'tty', which is placed below the 'special'
> rank but above the 'access' ranks.  This new rank is used only by the
> tty_lock, which formerly had 'event' rank.
> 
> This eliminates a rare lock rank inversion in
> nmethod::log_new_method, where the tty_lock is locked around a
> resolve of a jweak.  That resolve could require allocating a SATB
> buffer or enqueuing a full one, either of which will attempt to lock
> an 'access' mutex.  With the old ranks, that 'access' mutex has
> higher rank than the already owned tty_lock, asserting in a debug
> build, and potentially deadlocking in a product build.  (The deadlock
> scenario seems unlikely; see JDK-8214997 for a related scenario.)
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8214997
> 
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8214315/open.00/
> 
> Testing:
> mach5 tier1-5
> 

  looks good.

Thomas