linux/kernel/rcutree.c, branch v3.6

rcu: Fix code-style issues involving "else"

2012-07-06T13:01:48Z

The Linux kernel coding style says that single-statement blocks should omit curly braces unless the other leg of the "if" statement has multiple statements, in which case the curly braces should be included. This commit fixes RCU's violations of this rule. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

Merge branches 'bigrtm.2012.07.04a', 'doctorture.2012.07.02a', 'fixes.2012.07.06a' and 'fnh.2012.07.02a' into HEAD

2012-07-06T12:59:30Z

bigrtm: First steps towards getting RCU out of the way of tens-of-microseconds real-time response on systems compiled with NR_CPUS=4096. Also cleanups for and increased concurrency of rcu_barrier() family of primitives. doctorture: rcutorture and documentation improvements. fixes: Miscellaneous fixes. fnh: RCU_FAST_NO_HZ fixes and improvements.

rcu: Introduce check for callback list/count mismatch

2012-07-06T12:55:16Z

The recent bug that introduced the RCU callback list/count mismatch showed the need for a diagnostic to check for this, which this commit adds. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Dump only the current CPU's buffers for idle-entry/exit warnings

2012-07-02T19:34:42Z

Problems in RCU idle entry and exit are almost always confined to the offending CPU. This commit therefore switches ftrace_dump() from DUMP_ALL to DUMP_ORIG. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Heiko Carstens Tested-by: Pascal Chapperon

rcu: Add check for CPUs going offline with callbacks queued

2012-07-02T19:34:25Z

If a CPU goes offline with callbacks queued, those callbacks might be indefinitely postponed, which can result in a system hang. This commit therefore inserts warnings for this condition. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney

rcu: Disable preemption in rcu_blocking_is_gp()

2012-07-02T19:34:25Z

It is time to optimize CONFIG_TREE_PREEMPT_RCU's synchronize_rcu() for uniprocessor optimization, which means that rcu_blocking_is_gp() can no longer rely on RCU read-side critical sections having disabled preemption. This commit therefore disables preemption across rcu_blocking_is_gp()'s scan of the cpu_online_mask. (Updated from previous version to fix embarrassing bug spotted by Wu Fengguang.) Signed-off-by: Paul E. McKenney

rcu: Split RCU core processing out of __call_rcu()

2012-07-02T19:34:24Z

The __call_rcu() function is a bit overweight, so this commit splits it into actual enqueuing of and accounting for the callback (__call_rcu()) and associated RCU-core processing (__call_rcu_core()). Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Prevent __call_rcu() from invoking RCU core on offline CPUs

2012-07-02T19:34:24Z

The __call_rcu() function will invoke the RCU core, for example, if it detects that the current CPU has too many callbacks. However, this can happen on an offline CPU that is on its way to the idle loop, in which case it is an error to invoke the RCU core, and the excess callbacks will be adopted in any case. This commit therefore adds checks to __call_rcu() for running on an offline CPU, refraining from invoking the RCU core in this case. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Make __call_rcu() handle invocation from idle

2012-07-02T19:34:24Z

Although __call_rcu() is handled correctly when called from a momentary non-idle period, if it is called on a CPU that RCU believes to be idle on RCU_FAST_NO_HZ kernels, the callback might be indefinitely postponed. This commit therefore ensures that RCU is aware of the new callback and has a chance to force the CPU out of dyntick-idle mode when a new callback is posted. Reported-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Add ACCESS_ONCE() to ->qlen accesses

2012-07-02T19:34:22Z

The _rcu_barrier() function accesses other CPUs' rcu_data structure's ->qlen field without benefit of locking. This commit therefore adds the required ACCESS_ONCE() wrappers around accesses and updates that need it. ACCESS_ONCE() is not needed when a CPU accesses its own ->qlen, or in code that cannot run while _rcu_barrier() is sampling ->qlen fields. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett