linux/kernel/rcutree.c, branch v3.9

Merge branches 'doctorture.2013.01.29a', 'fixes.2013.01.26a', 'tagcb.2013.01.24a' and 'tiny.2013.01.29b' into HEAD

2013-01-29T06:25:21Z

doctorture.2013.01.11a: Changes to rcutorture and to RCU documentation. fixes.2013.01.26a: Miscellaneous fixes. tagcb.2013.01.24a: Tag RCU callbacks with grace-period number to simplify callback advancement. tiny.2013.01.29b: Enhancements to uniprocessor handling in tiny RCU.

rcu: Provide RCU CPU stall warnings for tiny RCU

2013-01-29T06:06:21Z

Tiny RCU has historically omitted RCU CPU stall warnings in order to reduce memory requirements, however, lack of these warnings caused Thomas Gleixner some debugging pain recently. Therefore, this commit adds RCU CPU stall warnings to tiny RCU if RCU_TRACE=y. This keeps the memory footprint small, while still enabling CPU stall warnings in kernels built to enable them. Updated to include Josh Triplett's suggested use of RCU_STALL_COMMON config variable to simplify #if expressions. Reported-by: Thomas Gleixner Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Remove unused code originally used for context tracking

2013-01-27T00:34:48Z

As context tracking subsystem evolved, it stopped using ignore_user_qs and in_user defined in the rcu_dynticks structure. This commit therefore removes them. Signed-off-by: Li Zhong Signed-off-by: Paul E. McKenney Acked-by: Frederic Weisbecker

rcu: Correct 'optimized' to 'optimize' in header comment

2013-01-27T00:34:13Z

Small grammar fix in rcutree comment regarding 'rcu_scheduler_active' var. Signed-off-by: Cody P Schafer Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Trace callback acceleration

2013-01-08T22:15:57Z

This commit adds event tracing for callback acceleration to allow better tracking of callbacks through the system. Signed-off-by: Paul E. McKenney

rcu: Tag callback lists with corresponding grace-period number

2013-01-08T22:15:57Z

Currently, callbacks are advanced each time the corresponding CPU notices a change in its leaf rcu_node structure's ->completed value (this value counts grace-period completions). This approach has worked quite well, but with the advent of RCU_FAST_NO_HZ, we cannot count on a given CPU seeing all the grace-period completions. When a CPU misses a grace-period completion that occurs while it is in dyntick-idle mode, this will delay invocation of its callbacks. In addition, acceleration of callbacks (when RCU realizes that a given callback need only wait until the end of the next grace period, rather than having to wait for a partial grace period followed by a full grace period) must be carried out extremely carefully. Insufficient acceleration will result in unnecessarily long grace-period latencies, while excessive acceleration will result in premature callback invocation. Changes that involve this tradeoff are therefore among the most nerve-wracking changes to RCU. This commit therefore explicitly tags groups of callbacks with the number of the grace period that they are waiting for. This means that callback-advancement and callback-acceleration functions are idempotent, so that excessive acceleration will merely waste a few CPU cycles. This also allows a CPU to take full advantage of any grace periods that have elapsed while it has been in dyntick-idle mode. It should also enable simulataneous simplifications to and optimizations of RCU_FAST_NO_HZ. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney

rcu: Silence compiler array out-of-bounds false positive

2013-01-08T22:15:25Z

It turns out that gcc 4.8 warns on array indexes being out of bounds unless it can prove otherwise. It gives this warning on some RCU initialization code. Because this is far from any fastpath, add an explicit check for array bounds and panic if so. This gives the compiler enough information to figure out that the array index is never out of bounds. However, if a similar false positive occurs on a fastpath, it will probably be necessary to tell the compiler to keep its array-index anxieties to itself. ;-) Markus Trippelsdorf Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Use new nesting value for rcu_dyntick trace in rcu_eqs_enter_common

2013-01-08T22:15:25Z

This patch uses the real new value of dynticks_nesting instead of 0 in rcu_eqs_enter_common(). Signed-off-by: Li Zhong Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Make rcu_is_cpu_rrupt_from_idle helper functions static

2013-01-08T22:15:25Z

Both rcutiny and rcutree define a helper function named rcu_is_cpu_rrupt_from_idle(), each used exactly once, later in the same file. This commit therefore declares these helper functions static. Signed-off-by: Josh Triplett Signed-off-by: Paul E. McKenney

context_tracking: New context tracking susbsystem

2012-11-30T19:40:07Z

Create a new subsystem that probes on kernel boundaries to keep track of the transitions between level contexts with two basic initial contexts: user or kernel. This is an abstraction of some RCU code that use such tracking to implement its userspace extended quiescent state. We need to pull this up from RCU into this new level of indirection because this tracking is also going to be used to implement an "on demand" generic virtual cputime accounting. A necessary step to shutdown the tick while still accounting the cputime. Signed-off-by: Frederic Weisbecker Cc: Andrew Morton Cc: H. Peter Anvin Cc: Ingo Molnar Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Li Zhong Cc: Gilad Ben-Yossef Reviewed-by: Steven Rostedt [ paulmck: fix whitespace error and email address. ] Signed-off-by: Paul E. McKenney