user/sven/linux.git/kernel/rcutiny.c, branch v3.4.44

rcu: Add RCU_NONIDLE() for idle-loop RCU read-side critical sections

2012-02-21T17:06:13Z

RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden in the inner idle loop, that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU will happily ignore any such read-side critical sections. However, things like powertop need tracepoints in the inner idle loop. This commit therefore provides an RCU_NONIDLE() macro that can be used to wrap code in the idle loop that requires RCU read-side critical sections. Suggested-by: Steven Rostedt Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Acked-by: Deepthi Dharwar

rcu: Allow nesting of rcu_idle_enter() and rcu_idle_exit()

2012-02-21T17:06:12Z

Use of RCU in the idle loop is incorrect, quite a few instances of just that have made their way into mainline, primarily event tracing. The problem with RCU read-side critical sections on CPUs that RCU believes to be idle is that RCU is completely ignoring the CPU, along with any attempts and RCU read-side critical sections. The approaches of eliminating the offending uses and of pushing the definition of idle down beyond the offending uses have both proved impractical. The new approach is to encapsulate offending uses of RCU with rcu_idle_exit() and rcu_idle_enter(), but this requires nesting for code that is invoked both during idle and and during normal execution. Therefore, this commit modifies rcu_idle_enter() and rcu_idle_exit() to permit nesting. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Acked-by: Deepthi Dharwar

rcu: Avoid waking up CPUs having only kfree_rcu() callbacks

2012-02-21T17:03:25Z

When CONFIG_RCU_FAST_NO_HZ is enabled, RCU will allow a given CPU to enter dyntick-idle mode even if it still has RCU callbacks queued. RCU avoids system hangs in this case by scheduling a timer for several jiffies in the future. However, if all of the callbacks on that CPU are from kfree_rcu(), there is no reason to wake the CPU up, as it is not a problem to defer freeing of memory. This commit therefore tracks the number of callbacks on a given CPU that are from kfree_rcu(), and avoids scheduling the timer if all of a given CPU's callbacks are from kfree_rcu(). Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney

rcu: Add lockdep-RCU checks for simple self-deadlock

2012-02-21T17:03:23Z

It is illegal to have a grace period within a same-flavor RCU read-side critical section, so this commit adds lockdep-RCU checks to splat when such abuse is encountered. This commit does not detect more elaborate RCU deadlock situations. These situations might be a job for lockdep enhancements. Signed-off-by: Paul E. McKenney

rcu: Augment rcu_batch_end tracing for idle and callback state

2011-12-11T18:32:22Z

The current rcu_batch_end event trace records only the name of the RCU flavor and the total number of callbacks that remain queued on the current CPU. This is insufficient for testing and tuning the new dyntick-idle RCU_FAST_NO_HZ code, so this commit adds idle state along with whether or not any of the callbacks that were ready to invoke at the beginning of rcu_do_batch() are still queued. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney

rcu: Make RCU use the new is_idle_task() API

2011-12-11T18:31:48Z

Change from direct comparison of ->pid with zero to is_idle_task(). Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Fix idle-task checks

2011-12-11T18:31:44Z

RCU has traditionally relied on idle_cpu() to determine whether a given CPU is running in the context of an idle task, but commit 908a3283 (Fix idle_cpu()) has invalidated this approach. After commit 908a3283, idle_cpu() will return true if the current CPU is currently running the idle task, and will be doing so for the foreseeable future. RCU instead needs to know whether or not the current CPU is currently running the idle task, regardless of what the near future might bring. This commit therefore switches from idle_cpu() to "current->pid != 0". Reported-by: Wu Fengguang Suggested-by: Carsten Emde Signed-off-by: Paul E. McKenney Acked-by: Steven Rostedt Tested-by: Wu Fengguang Signed-off-by: Paul E. McKenney

rcu: Add more information to the wrong-idle-task complaint

2011-12-11T18:31:42Z

The current code just complains if the current task is not the idle task. This commit therefore adds printing of the identity of the idle task. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Deconfuse dynticks entry-exit tracing

2011-12-11T18:31:42Z

The trace_rcu_dyntick() trace event did not print both the old and the new value of the nesting level, and furthermore printed only the low-order 32 bits of it. This could result in some confusion when interpreting trace-event dumps, so this commit prints both the old and the new value, prints the full 64 bits, and also selects the process-entry/exit increment to print nicely in hexadecimal. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Detect illegal rcu dereference in extended quiescent state

2011-12-11T18:31:30Z

Report that none of the rcu read lock maps are held while in an RCU extended quiescent state (the section between rcu_idle_enter() and rcu_idle_exit()). This helps detect any use of rcu_dereference() and friends from within the section in idle where RCU is not allowed. This way we can guarantee an extended quiescent window where the CPU can be put in dyntick idle mode or can simply aoid to be part of any global grace period completion while in the idle loop. Uses of RCU from such mode are totally ignored by RCU, hence the importance of these checks. Signed-off-by: Frederic Weisbecker Cc: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Lai Jiangshan Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett