Messages in this thread | | | Date | Fri, 30 Oct 2009 19:42:42 -0700 | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 0/3] rcu: clean up locking for ->completed and ->gpnum fields |
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Hello!
This patch series imposes a clear locking model on accesses to the ->completed and ->gpnum fields, significantly increasing the reliability of RCU. To be fair, in order to induce failures in current -tip, you have to run long rcutorture tests on particular hardware with particular kernel configuration parameters, while having modified the RCU implementation itself to invoke force_quiescent_state() several times as often as normal. By "particular hardware", I do mean specific machines that appear otherwise identical to other machines with much lower (and sometimes even nonexistent) failure rates. After all, these are race conditions, and as such can be affected by very subtle factors.
That said, RCU really needs to stand up to whatever abuse shows up, hence these patches.
1. The first patch puts non-NO_HZ accesses to the ->completed field under a well-defined locking design, eliminating the unsynchronized accesses to rsp->completed from the dyntick_recall_completed() function.
2. The second patch puts the rcu_process_gp_end() function's use of the ->completed field under a well-defined locking design, eliminating its previously unsynchronized accesses to rsp->completed.
3. The third and final patch puts accesses to the ->gpnum field under a well-defined locking design, eliminating the unsynchronized accesses to rsp->gpnum from the note_new_gpnum() function.
A number of unsynchronized accesses remain, but these are of the form of an unsynchronized check followed by a lock acquisition followed by a repeat of the check.
Thanx, Paul
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