rcu/nocb: Use separate flag to indicate disabled ->cblist

NULLing the RCU_NEXT_TAIL pointer was a clever way to save a byte, but
forward-progress considerations would require that this pointer be both
NULL and non-NULL, which, absent a quantum-computer port of the Linux
kernel, simply won't happen.  This commit therefore creates as separate
->enabled flag to replace the current NULL checks.

[ paulmck: Add include files per 0day test robot and -next. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
index 87404cb..ed2cfd3 100644 (file)
--- a/include/linux/rcu_segcblist.h
+++ b/include/linux/rcu_segcblist.h
@@ -14,6 +14,9 @@
 #ifndef __INCLUDE_LINUX_RCU_SEGCBLIST_H
 #define __INCLUDE_LINUX_RCU_SEGCBLIST_H
 
+#include <linux/types.h>
+#include <linux/atomic.h>
+
 /* Simple unsegmented callback lists. */
 struct rcu_cblist {
        struct rcu_head *head;
@@ -67,6 +70,7 @@ struct rcu_segcblist {
        unsigned long gp_seq[RCU_CBLIST_NSEGS];
        long len;
        long len_lazy;
+       u8 enabled;
 };
 
 #define RCU_SEGCBLIST_INITIALIZER(n) \

diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 9bd5f60..b305dca 100644 (file)
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -58,6 +58,7 @@ void rcu_segcblist_init(struct rcu_segcblist *rsclp)
                rsclp->tails[i] = &rsclp->head;
        rsclp->len = 0;
        rsclp->len_lazy = 0;
+       rsclp->enabled = 1;
 }
 
 /*
@@ -69,7 +70,7 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
        WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
        WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
        WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
-       rsclp->tails[RCU_NEXT_TAIL] = NULL;
+       rsclp->enabled = 0;
 }
 
 /*

diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 822a39d..b2de7b3 100644 (file)
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -63,7 +63,7 @@ static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
  */
 static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
 {
-       return !!rsclp->tails[RCU_NEXT_TAIL];
+       return rsclp->enabled;
 }
 
 /*

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0a3f868..b8a43cf 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2189,8 +2189,8 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
                                rcu_segcblist_n_cbs(&rdp->cblist));
                atomic_long_set(&rdp->nocb_q_count_lazy,
                                rcu_segcblist_n_lazy_cbs(&rdp->cblist));
-               rcu_segcblist_init(&rdp->cblist);
        }
+       rcu_segcblist_init(&rdp->cblist);
        rcu_segcblist_disable(&rdp->cblist);
        return true;
 }