linux/kernel/rcu, branch v4.3

rcu: Suppress lockdep false positive for rcp->exp_funnel_mutex

2015-09-21T04:01:22Z

In kernels built with CONFIG_PREEMPT=y, synchronize_rcu_expedited() invokes synchronize_sched_expedited() while holding RCU-preempt's root rcu_node structure's ->exp_funnel_mutex, which is acquired after the rcu_data structure's ->exp_funnel_mutex. The first thing that synchronize_sched_expedited() will do is acquire RCU-sched's rcu_data structure's ->exp_funnel_mutex. There is no danger of an actual deadlock because the locking order is always from RCU-preempt's expedited mutexes to those of RCU-sched. Unfortunately, lockdep considers both rcu_data structures' ->exp_funnel_mutex to be in the same lock class and therefore reports a deadlock cycle. This commit silences this false positive by placing RCU-sched's rcu_data structures' ->exp_funnel_mutex locks into their own lock class. Reported-by: Sasha Levin Signed-off-by: Paul E. McKenney

rcu,locking: Privatize smp_mb__after_unlock_lock()

2015-08-04T15:49:21Z

RCU is the only thing that uses smp_mb__after_unlock_lock(), and is likely the only thing that ever will use it, so this commit makes this macro private to RCU. Signed-off-by: Paul E. McKenney Cc: Will Deacon Cc: Peter Zijlstra Cc: Benjamin Herrenschmidt Cc: "linux-arch@vger.kernel.org"

Merge branches 'doc.2015.07.15a' and 'torture.2015.07.15a' into HEAD

2015-08-04T15:42:02Z

doc.2015.07.15a: Documentation updates. torture.2015.07.15a: Torture-test updates.

Merge branches 'fixes.2015.07.22a' and 'initexp.2015.08.04a' into HEAD

2015-08-04T15:40:58Z

fixes.2015.07.22a: Miscellaneous fixes. initexp.2015.08.04a: Initialization and expedited updates. (Single branch due to conflicts.)

rcu: Silence lockdep false positive for expedited grace periods

2015-08-04T15:39:21Z

In a CONFIG_PREEMPT=y kernel, synchronize_rcu_expedited() acquires the ->exp_funnel_mutex in rcu_preempt_state, then invokes synchronize_sched_expedited, which acquires the ->exp_funnel_mutex in rcu_sched_state. There can be no deadlock because rcu_preempt_state ->exp_funnel_mutex acquisition always precedes that of rcu_sched_state. But lockdep does not know that, so it gives false-positive splats. This commit therefore associates a separate lock_class_key structure with the rcu_sched_state structure's ->exp_funnel_mutex, allowing lockdep to see the lock ordering, avoiding the false positives. Signed-off-by: Paul E. McKenney

rcu: Don't disable CPU hotplug during OOM notifiers

2015-07-22T22:27:43Z

RCU's rcu_oom_notify() disables CPU hotplug in order to stabilize the list of online CPUs, which it traverses. However, this is completely pointless because smp_call_function_single() will quietly fail if invoked on an offline CPU. Because the count of requests is incremented in the rcu_oom_notify_cpu() function that is remotely invoked, everything works nicely even in the face of concurrent CPU-hotplug operations. Furthermore, in recent kernels, invoking get_online_cpus() from an OOM notifier can result in deadlock. This commit therefore removes the call to get_online_cpus() and put_online_cpus() from rcu_oom_notify(). Reported-by: Marcin Ślusarz Reported-by: David Rientjes Signed-off-by: Paul E. McKenney Acked-by: David Rientjes Tested-by: Marcin Ślusarz

rcu: Fix backwards RCU_LOCKDEP_WARN() in synchronize_rcu_tasks()

2015-07-22T22:27:33Z

The RCU_LOCKDEP_WARN() in synchronize_rcu_tasks() triggers if the scheduler is active, which is backwards. This commit therefore negates the test. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney

rcu: Rename rcu_lockdep_assert() to RCU_LOCKDEP_WARN()

2015-07-22T22:27:32Z

This commit renames rcu_lockdep_assert() to RCU_LOCKDEP_WARN() for consistency with the WARN() series of macros. This also requires inverting the sense of the conditional, which this commit also does. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney Reviewed-by: Ingo Molnar

rcu: Make rcu_is_watching() really notrace

2015-07-22T22:27:31Z

Although rcu_is_watching() is marked notrace, it invokes preempt_disable() and preempt_enable(), both of which can be traced. This defeats the purpose of the notrace on rcu_is_watching(), so this commit substitutes preempt_disable_notrace() and preempt_enable_notrace(). Signed-off-by: Alexei Starovoitov Signed-off-by: Paul E. McKenney Acked-by: Steven Rostedt

rcu: Create a synchronize_rcu_mult()

2015-07-22T22:27:29Z

There have been several requests for a primitive that waits for grace periods for several RCU flavors concurrently, so this commit creates it. This is a variadic macro, and you pass in the call_rcu() functions of the flavors of RCU that you wish to wait for. Note that you cannot pass in call_srcu() for two reasons: (1) This would result in a type mismatch and (2) You need to specify which srcu_struct you want to use. Handle this by creating a wrapper function for your SRCU domain, for example: void call_srcu_mine(struct rcu_head *head, rcu_callback_t func) { call_srcu(&ss_mine, head, func); } You can then do something like this: synchronize_rcu_mult(call_srcu_mine, call_rcu, call_rcu_sched); Signed-off-by: Paul E. McKenney