rcu: Use simple wait queues where possible in rcutree

As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads
GP waits") the RCU subsystem started making use of wait queues.

Here we convert all additions of RCU wait queues to use simple wait queues,
since they don't need the extra overhead of the full wait queue features.

Originally this was done for RT kernels[1], since we would get things like...

  BUG: sleeping function called from invalid context at kernel/rtmutex.c:659
  in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt
  Pid: 8, comm: rcu_preempt Not tainted
  Call Trace:
   [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0
   [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50
   [<ffffffff8106fcf6>] __wake_up+0x36/0x70
   [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680
   [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50
   [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80
   [<ffffffff8105eabb>] kthread+0xdb/0xe0
   [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100
   [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10
   [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60
   [<ffffffff817e0750>] ? gs_change+0xb/0xb

...and hence simple wait queues were deployed on RT out of necessity
(as simple wait uses a raw lock), but mainline might as well take
advantage of the more streamline support as well.

[1] This is a carry forward of work from v3.10-rt; the original conversion
was by Thomas on an earlier -rt version, and Sebastian extended it to
additional post-3.10 added RCU waiters; here I've added a commit log and
unified the RCU changes into one, and uprev'd it to match mainline RCU.

Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-rt-users@vger.kernel.org
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1455871601-27484-6-git-send-email-wagi@monom.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 7 insertions, 6 deletions

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 10dedfbef09d..bbd235d0e71f 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -27,6 +27,7 @@
 #include <linux/threads.h>
 #include <linux/cpumask.h>
 #include <linux/seqlock.h>
+#include <linux/swait.h>
 #include <linux/stop_machine.h>
 
 /*
@@ -243,7 +244,7 @@ struct rcu_node {
                                 /* Refused to boost: not sure why, though. */
                                 /*  This can happen due to race conditions. */
 #ifdef CONFIG_RCU_NOCB_CPU
-        wait_queue_head_t nocb_gp_wq[2];
+        struct swait_queue_head nocb_gp_wq[2];
                                 /* Place for rcu_nocb_kthread() to wait GP. */
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
         int need_future_gp[2];
@@ -399,7 +400,7 @@ struct rcu_data {
         atomic_long_t nocb_q_count_lazy; /*  invocation (all stages). */
         struct rcu_head *nocb_follower_head; /* CBs ready to invoke. */
         struct rcu_head **nocb_follower_tail;
-        wait_queue_head_t nocb_wq;      /* For nocb kthreads to sleep on. */
+        struct swait_queue_head nocb_wq; /* For nocb kthreads to sleep on. */
         struct task_struct *nocb_kthread;
         int nocb_defer_wakeup;          /* Defer wakeup of nocb_kthread. */
 
@@ -478,7 +479,7 @@ struct rcu_state {
         unsigned long gpnum;                    /* Current gp number. */
         unsigned long completed;                /* # of last completed gp. */
         struct task_struct *gp_kthread;         /* Task for grace periods. */
-        wait_queue_head_t gp_wq;                /* Where GP task waits. */
+        struct swait_queue_head gp_wq;          /* Where GP task waits. */
         short gp_flags;                         /* Commands for GP task. */
         short gp_state;                         /* GP kthread sleep state. */
 
@@ -506,7 +507,7 @@ struct rcu_state {
         unsigned long expedited_sequence;       /* Take a ticket. */
         atomic_long_t expedited_normal;         /* # fallbacks to normal. */
         atomic_t expedited_need_qs;             /* # CPUs left to check in. */
-        wait_queue_head_t expedited_wq;         /* Wait for check-ins. */
+        struct swait_queue_head expedited_wq;   /* Wait for check-ins. */
         int ncpus_snap;                         /* # CPUs seen last time. */
 
         unsigned long jiffies_force_qs;         /* Time at which to invoke */
@@ -621,8 +622,8 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp);
 static void increment_cpu_stall_ticks(void);
 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu);
 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq);
-static wait_queue_head_t *rcu_nocb_gp_get(struct rcu_node *rnp);
-static void rcu_nocb_gp_cleanup(wait_queue_head_t *sq);
+static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
+static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
 static void rcu_init_one_nocb(struct rcu_node *rnp);
 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
                             bool lazy, unsigned long flags);