Messages in this thread | | | Date | Thu, 6 Jul 2006 10:14:01 -0700 | From | "Paul E. McKenney" <> | Subject | [PATCH 0/2] srcu-3: add RCU variant that permits read-side blocking |
| |
Version 3 of the SRCU patchset.
This patch incorporates a number of improvements, many of which came up in off-list discussions with Alan Stern. Neither of us are sure why these discussions ended up off-list, so I have summarized them below.
o Fixes some "zombie code" -- excess curly braces and the like.
o Gets rid of the double-flip in favor of an additional synchronize_sched(). This turned out to be safe, despite my saying otherwise at http://lkml.org/lkml/2006/6/27/486. The trick that I was missing is that synchronize_sched() forces all CPUs to execute at least one memory barrier during the synchronize_sched()'s execution, which forces all CPUs to see synchronize_srcu()'s counter increment as happening after any memory manipulations prior to the synchronize_srcu().
Upgraded comments to indicate what the synchronize_sched() calls are needed for.
o Added a barrier() to both srcu_read_lock() and srcu_read_unlock() to prevent the compiler from performing optimizations that would cause the critical section to move outside of the enclosing srcu_read_lock() and srcu_read_unlock().
However, these barrier()s in srcu_read_lock() and srcu_read_unlock() are needed only in non-CONFIG_PREEMPT kernels, so they compile to nothing in CONFIG_PREEMPT kernels (where the preempt_disable() and preempt_enable() calls supply the needed barrier() call).
o Added a check to synchronize_srcu() that permits this primitive to take advantage of grace periods induced by concurrent executions in other tasks. This can be useful in cases where you are using a single srcu_struct to handle all the individually-locked chains of a hash table, for example.
o cleanup_srcu_struct() now contains error checks to catch cases where readers are still using the srcu_struct in question. It does a WARN_ON() and leaks the srcu_struct's per-CPU data in that case.
o There is an srcu_readers_active() that returns the number of readers (approximate!) currently using the specified srcu_struct. This can be useful when terminating use of an srcu_struct, e.g., at module-unload time.
o Improved the RCU torture tests, increasing the skew on reader times and providing implementation-specific delay functions. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |