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>

Paul E. McKenney committed 7 years ago

Commit 1bb5f9b1 parent 18cd8c94 files · +8 −3Browse files

Unified · Split

4 files

include/linux/rcu_segcblist.h +4 −0
kernel/rcu/rcu_segcblist.c +2 −1
kernel/rcu/rcu_segcblist.h +1 −1
kernel/rcu/tree_plugin.h +1 −1

include/linux/rcu_segcblist.h+4−0

@@ -14,6 +14,9 @@ · 13 unmodified lines
14	14	#ifndef __INCLUDE_LINUX_RCU_SEGCBLIST_H
15	15	#define __INCLUDE_LINUX_RCU_SEGCBLIST_H
16	16
	17	+#include <linux/types.h>
	18	+#include <linux/atomic.h>
	19	+
17	20	/* Simple unsegmented callback lists. */
18	21	struct rcu_cblist {
19	22	struct rcu_head *head;
@@ -67,6 +70,7 @@ struct rcu_segcblist { · 47 unmodified lines
67	70	unsigned long gp_seq[RCU_CBLIST_NSEGS];
68	71	long len;
69	72	long len_lazy;
	73	+ u8 enabled;
70	74	};
71	75
72	76	#define RCU_SEGCBLIST_INITIALIZER(n) \

kernel/rcu/rcu_segcblist.c+2−1

@@ -58,6 +58,7 @@ void rcu_segcblist_init(struct rcu_segcblist *rsclp) · 57 unmodified lines
58	58	rsclp->tails[i] = &rsclp->head;
59	59	rsclp->len = 0;
60	60	rsclp->len_lazy = 0;
	61	+ rsclp->enabled = 1;
61	62	}
62	63
63	64	/*
@@ -69,7 +70,7 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp) · 5 unmodified lines
69	70	WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
70	71	WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
71	72	WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
72		− rsclp->tails[RCU_NEXT_TAIL] = NULL;
	73	+ rsclp->enabled = 0;
73	74	}
74	75
75	76	/*

kernel/rcu/rcu_segcblist.h+1−1

@@ -63,7 +63,7 @@ static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp) · 62 unmodified lines
63	63	*/
64	64	static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
65	65	{
66		− return !!rsclp->tails[RCU_NEXT_TAIL];
	66	+ return rsclp->enabled;
67	67	}
68	68
69	69	/*

kernel/rcu/tree_plugin.h+1−1

@@ -2189,8 +2189,8 @@ static bool init_nocb_callback_list(struct rcu_data *rdp) · 2188 unmodified lines
2189	2189	rcu_segcblist_n_cbs(&rdp->cblist));
2190	2190	atomic_long_set(&rdp->nocb_q_count_lazy,
2191	2191	rcu_segcblist_n_lazy_cbs(&rdp->cblist));
2192		− rcu_segcblist_init(&rdp->cblist);
2193	2192	}
	2193	+ rcu_segcblist_init(&rdp->cblist);
2194	2194	rcu_segcblist_disable(&rdp->cblist);
2195	2195	return true;
2196	2196	}

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

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