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

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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>
This commit is contained in:
Paul E. McKenney 2019-04-12 12:34:41 -07:00
parent 18cd8c93e6
commit 1bb5f9b95a
4 changed files with 8 additions and 3 deletions
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4
include/linux/rcu_segcblist.h
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@ -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) \

3
kernel/rcu/rcu_segcblist.c
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@ -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;
}
/*

2
kernel/rcu/rcu_segcblist.h
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@ -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;
}
/*

2
kernel/rcu/tree_plugin.h
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@ -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;
}