linux/Documentation/RCU, branch v4.5

documentation: Update RCU requirements based on expedited changes

2015-12-05T20:34:32Z

Because RCU-sched expedited grace periods now use IPIs and interact with rcu_read_unlock(), it is no longer sufficient to disable preemption across RCU read-side critical sections that acquire and hold scheduler locks. It is now necessary to instead disable interrupts. This commit documents this change. Signed-off-by: Paul E. McKenney

documentation: Clarify RCU memory barriers and requirements

2015-12-05T20:33:37Z

The RCU requirements do not make it absolutely clear that the memory-barrier requirements are not intended to replace the fundamental requirement that all pre-existing RCU readers complete before a grace period completes. This commit therefore pulls the memory-barrier requirements into a separate section and explicitly calls out the relationship between the memory-barrier requirements and the fundamental requirement. Signed-off-by: Paul E. McKenney

documentation: Expand on scheduler/RCU deadlock requirements

2015-12-05T20:33:26Z

This commit adds a second option for avoiding scheduler/RCU deadlocks, namely that preemption be disabled across the entire RCU read-side critical section in question. Signed-off-by: Paul E. McKenney

documentation: Composability analogies

2015-12-05T20:33:11Z

This commit expands on RCU's composability by comparing it to that of transactional memory and of locking. Signed-off-by: Paul E. McKenney

documentation: Cover requirements controlling stall warnings

2015-12-05T20:32:19Z

This commit adds verbiage on boot and sysfs parameters that can be used to control RCU CPU stall warnings, both to change the timeout and to suppress these warnings entirely. Signed-off-by: Paul E. McKenney

Documentation: Record bottom-bit-zero guarantee for ->next

2015-12-05T20:31:47Z

This commit records RCU's guarantee that the bottom bit of the rcu_head structure's ->next field will remain zero for callbacks posted via call_rcu(), but not necessarily for kfree_rcu() or some possible future call_rcu_lazy() variant that might one day be created for energy-efficiency purposese. Signed-off-by: Paul E. McKenney [ paulmck: Updates URLs as suggested by Josh Triplett. ]

documentation: Record RCU requirements

2015-12-05T20:19:07Z

This commit adds RCU requirements as published in a 2015 LWN series. Bringing these requirements in-tree allows them to be updated as changes are discovered. Signed-off-by: Paul E. McKenney [ paulmck: Updates to charset and URLs as suggested by Josh Triplett. ]

Merge branches 'doc.2015.10.06a', 'percpu-rwsem.2015.10.06a' and 'torture.2015.10.06a' into HEAD

2015-10-07T23:06:25Z

doc.2015.10.06a: Documentation updates. percpu-rwsem.2015.10.06a: Optimization of per-CPU reader-writer semaphores. torture.2015.10.06a: Torture-test updates.

documentation: Catch up list of torture_type options

2015-10-06T18:22:48Z

This commit rids the documentation of long-obsolete torture_type options such as rcu_sync and adds new ones such as tasks. Also add verbiage noting the fact that rcutorture now concurrently tests the asynchrounous, synchronous, expedited synchronous, and polling grace-period primitives. Reported-by: David Miller Signed-off-by: Paul E. McKenney Acked-by: David Miller Reviewed-by: Josh Triplett

documentation: Correct doc to use rcu_dereference_protected

2015-10-06T18:22:43Z

As there is lots of misinformation and outdated information on the Internet about nearly all topics related to the kernel, I thought it would be best if I based my RCU code on the guidelines of the examples in the Documentation/ tree of the latest kernel. One thing that stuck out when reading the whatisRCU.txt document was, "interesting how we don't need any function to dereference rcu protected pointers when doing updates if a lock is held. I wonder how static analyzers will work with that." Then, a few weeks later, upon discovering sparse's __rcu support, I ran it over my code, and lo and behold, things weren't done right. Examining other RCU usages in the kernel reveal consistent usage of rcu_dereference_protected, passing in lockdep_is_held as the conditional. So, this patch adds that idiom to the documentation, so that others ahead of me won't endure the same exercise. Signed-off-by: Jason A. Donenfeld Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett