1 files changed, 271 insertions, 0 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
new file mode 100644
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+++ b/include/linux/rcupdate.h
@@ -0,0 +1,271 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion 
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2001
+ *
+ * Author: Dipankar Sarma <dipankar@in.ibm.com>
+ * 
+ * Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ *              http://lse.sourceforge.net/locking/rcupdate.html
+ *
+ */
+
+#ifndef __LINUX_RCUPDATE_H
+#define __LINUX_RCUPDATE_H
+
+#ifdef __KERNEL__
+
+#include <linux/cache.h>
+#include <linux/spinlock.h>
+#include <linux/threads.h>
+#include <linux/percpu.h>
+#include <linux/cpumask.h>
+#include <linux/seqlock.h>
+
+/**
+ * struct rcu_head - callback structure for use with RCU
+ * @next: next update requests in a list
+ * @func: actual update function to call after the grace period.
+ */
+struct rcu_head {
+        struct rcu_head *next;
+        void (*func)(struct rcu_head *head);
+};
+
+#define RCU_HEAD_INIT(head) { .next = NULL, .func = NULL }
+#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head)
+#define INIT_RCU_HEAD(ptr) do { \
+       (ptr)->next = NULL; (ptr)->func = NULL; \
+} while (0)
+
+
+
+/* Global control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+        long    cur;            /* Current batch number.                      */
+        long    completed;      /* Number of the last completed batch         */
+        int     next_pending;   /* Is the next batch already waiting?         */
+} ____cacheline_maxaligned_in_smp;
+
+/* Is batch a before batch b ? */
+static inline int rcu_batch_before(long a, long b)
+{
+        return (a - b) < 0;
+}
+
+/* Is batch a after batch b ? */
+static inline int rcu_batch_after(long a, long b)
+{
+        return (a - b) > 0;
+}
+
+/*
+ * Per-CPU data for Read-Copy UPdate.
+ * nxtlist - new callbacks are added here
+ * curlist - current batch for which quiescent cycle started if any
+ */
+struct rcu_data {
+        /* 1) quiescent state handling : */
+        long            quiescbatch;     /* Batch # for grace period */
+        int             passed_quiesc;   /* User-mode/idle loop etc. */
+        int             qs_pending;      /* core waits for quiesc state */
+
+        /* 2) batch handling */
+        long            batch;           /* Batch # for current RCU batch */
+        struct rcu_head *nxtlist;
+        struct rcu_head **nxttail;
+        struct rcu_head *curlist;
+        struct rcu_head **curtail;
+        struct rcu_head *donelist;
+        struct rcu_head **donetail;
+        int cpu;
+};
+
+DECLARE_PER_CPU(struct rcu_data, rcu_data);
+DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
+extern struct rcu_ctrlblk rcu_ctrlblk;
+extern struct rcu_ctrlblk rcu_bh_ctrlblk;
+
+/*
+ * Increment the quiescent state counter.
+ * The counter is a bit degenerated: We do not need to know
+ * how many quiescent states passed, just if there was at least
+ * one since the start of the grace period. Thus just a flag.
+ */
+static inline void rcu_qsctr_inc(int cpu)
+{
+        struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+        rdp->passed_quiesc = 1;
+}
+static inline void rcu_bh_qsctr_inc(int cpu)
+{
+        struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
+        rdp->passed_quiesc = 1;
+}
+
+static inline int __rcu_pending(struct rcu_ctrlblk *rcp,
+                                                struct rcu_data *rdp)
+{
+        /* This cpu has pending rcu entries and the grace period
+         * for them has completed.
+         */
+        if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
+                return 1;
+
+        /* This cpu has no pending entries, but there are new entries */
+        if (!rdp->curlist && rdp->nxtlist)
+                return 1;
+
+        /* This cpu has finished callbacks to invoke */
+        if (rdp->donelist)
+                return 1;
+
+        /* The rcu core waits for a quiescent state from the cpu */
+        if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
+                return 1;
+
+        /* nothing to do */
+        return 0;
+}
+
+static inline int rcu_pending(int cpu)
+{
+        return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
+                __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
+}
+
+/**
+ * rcu_read_lock - mark the beginning of an RCU read-side critical section.
+ *
+ * When synchronize_kernel() is invoked on one CPU while other CPUs
+ * are within RCU read-side critical sections, then the
+ * synchronize_kernel() is guaranteed to block until after all the other
+ * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
+ * on one CPU while other CPUs are within RCU read-side critical
+ * sections, invocation of the corresponding RCU callback is deferred
+ * until after the all the other CPUs exit their critical sections.
+ *
+ * Note, however, that RCU callbacks are permitted to run concurrently
+ * with RCU read-side critical sections.  One way that this can happen
+ * is via the following sequence of events: (1) CPU 0 enters an RCU
+ * read-side critical section, (2) CPU 1 invokes call_rcu() to register
+ * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
+ * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
+ * callback is invoked.  This is legal, because the RCU read-side critical
+ * section that was running concurrently with the call_rcu() (and which
+ * therefore might be referencing something that the corresponding RCU
+ * callback would free up) has completed before the corresponding
+ * RCU callback is invoked.
+ *
+ * RCU read-side critical sections may be nested.  Any deferred actions
+ * will be deferred until the outermost RCU read-side critical section
+ * completes.
+ *
+ * It is illegal to block while in an RCU read-side critical section.
+ */
+#define rcu_read_lock()         preempt_disable()
+
+/**
+ * rcu_read_unlock - marks the end of an RCU read-side critical section.
+ *
+ * See rcu_read_lock() for more information.
+ */
+#define rcu_read_unlock()       preempt_enable()
+
+/*
+ * So where is rcu_write_lock()?  It does not exist, as there is no
+ * way for writers to lock out RCU readers.  This is a feature, not
+ * a bug -- this property is what provides RCU's performance benefits.
+ * Of course, writers must coordinate with each other.  The normal
+ * spinlock primitives work well for this, but any other technique may be
+ * used as well.  RCU does not care how the writers keep out of each
+ * others' way, as long as they do so.
+ */
+
+/**
+ * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
+ *
+ * This is equivalent of rcu_read_lock(), but to be used when updates
+ * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
+ * consider completion of a softirq handler to be a quiescent state,
+ * a process in RCU read-side critical section must be protected by
+ * disabling softirqs. Read-side critical sections in interrupt context
+ * can use just rcu_read_lock().
+ *
+ */
+#define rcu_read_lock_bh()      local_bh_disable()
+
+/*
+ * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
+ *
+ * See rcu_read_lock_bh() for more information.
+ */
+#define rcu_read_unlock_bh()    local_bh_enable()
+
+/**
+ * rcu_dereference - fetch an RCU-protected pointer in an
+ * RCU read-side critical section.  This pointer may later
+ * be safely dereferenced.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (currently only the Alpha), and, more importantly, documents
+ * exactly which pointers are protected by RCU.
+ */
+
+#define rcu_dereference(p)     ({ \
+                                typeof(p) _________p1 = p; \
+                                smp_read_barrier_depends(); \
+                                (_________p1); \
+                                })
+
+/**
+ * rcu_assign_pointer - assign (publicize) a pointer to a newly
+ * initialized structure that will be dereferenced by RCU read-side
+ * critical sections.  Returns the value assigned.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (pretty much all of them other than x86), and also prevents
+ * the compiler from reordering the code that initializes the
+ * structure after the pointer assignment.  More importantly, this
+ * call documents which pointers will be dereferenced by RCU read-side
+ * code.
+ */
+
+#define rcu_assign_pointer(p, v)        ({ \
+                                                smp_wmb(); \
+                                                (p) = (v); \
+                                        })
+
+extern void rcu_init(void);
+extern void rcu_check_callbacks(int cpu, int user);
+extern void rcu_restart_cpu(int cpu);
+
+/* Exported interfaces */
+extern void FASTCALL(call_rcu(struct rcu_head *head, 
+                                void (*func)(struct rcu_head *head)));
+extern void FASTCALL(call_rcu_bh(struct rcu_head *head,
+                                void (*func)(struct rcu_head *head)));
+extern void synchronize_kernel(void);
+
+#endif /* __KERNEL__ */
+#endif /* __LINUX_RCUPDATE_H */