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Subject[tip:core/urgent] rcu: Clean up code based on review feedback from Josh Triplett, part 2
Commit-ID:  1eba8f84380bede3c602bd7758dea96925cead01
Gitweb: http://git.kernel.org/tip/1eba8f84380bede3c602bd7758dea96925cead01
Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Wed, 23 Sep 2009 09:50:42 -0700
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 23 Sep 2009 19:46:29 +0200

rcu: Clean up code based on review feedback from Josh Triplett, part 2

These issues identified during an old-fashioned face-to-face code
review extending over many hours.

o Add comments for tricky parts of code, and correct comments
that have passed their sell-by date.

o Get rid of the vestiges of rcu_init_sched(), which is no
longer needed now that PREEMPT_RCU is gone.

o Move the #include of rcutree_plugin.h to the end of
rcutree.c, which means that, rather than having a random
collection of forward declarations, the new set of forward
declarations document the set of plugins. The new home for
this #include also allows __rcu_init_preempt() to move into
rcutree_plugin.h.

o Fix rcu_preempt_check_callbacks() to be static.

Suggested-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12537246443924-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Peter Zijlstra <peterz@infradead.org>


---
include/linux/rcupdate.h | 4 ++
include/linux/rcutree.h | 6 +---
init/main.c | 1 -
kernel/rcutree.c | 72 +++++++++++++++++++++-------------------------
kernel/rcutree.h | 31 ++++++++++++++-----
kernel/rcutree_plugin.h | 23 +++++++++++++-
6 files changed, 82 insertions(+), 55 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 6fe0363..7033121 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -196,6 +196,8 @@ static inline void rcu_read_lock_sched(void)
__acquire(RCU_SCHED);
rcu_read_acquire();
}
+
+/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
static inline notrace void rcu_read_lock_sched_notrace(void)
{
preempt_disable_notrace();
@@ -213,6 +215,8 @@ static inline void rcu_read_unlock_sched(void)
__release(RCU_SCHED);
preempt_enable();
}
+
+/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
static inline notrace void rcu_read_unlock_sched_notrace(void)
{
__release(RCU_SCHED);
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 88109c8..19a3b06 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -90,10 +90,6 @@ extern long rcu_batches_completed(void);
extern long rcu_batches_completed_bh(void);
extern long rcu_batches_completed_sched(void);

-static inline void rcu_init_sched(void)
-{
-}
-
#ifdef CONFIG_NO_HZ
void rcu_enter_nohz(void);
void rcu_exit_nohz(void);
@@ -106,7 +102,7 @@ static inline void rcu_exit_nohz(void)
}
#endif /* CONFIG_NO_HZ */

-/* A context switch is a grace period for rcutree. */
+/* A context switch is a grace period for RCU-sched and RCU-bh. */
static inline int rcu_blocking_is_gp(void)
{
return num_online_cpus() == 1;
diff --git a/init/main.c b/init/main.c
index 34971be..833d675 100644
--- a/init/main.c
+++ b/init/main.c
@@ -782,7 +782,6 @@ static void __init do_initcalls(void)
*/
static void __init do_basic_setup(void)
{
- rcu_init_sched(); /* needed by module_init stage. */
init_workqueues();
cpuset_init_smp();
usermodehelper_init();
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f85b684..53a5ef0 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -81,24 +81,29 @@ DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);

-extern long rcu_batches_completed_sched(void);
-static struct rcu_node *rcu_get_root(struct rcu_state *rsp);
-static void cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp,
- struct rcu_node *rnp, unsigned long flags);
-static void cpu_quiet_msk_finish(struct rcu_state *rsp, unsigned long flags);
+/* Forward declarations for rcutree_plugin.h */
+static inline void rcu_bootup_announce(void);
+long rcu_batches_completed(void);
+static void rcu_preempt_note_context_switch(int cpu);
+static int rcu_preempted_readers(struct rcu_node *rnp);
+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+static void rcu_print_task_stall(struct rcu_node *rnp);
+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
-static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp);
+static void rcu_preempt_offline_tasks(struct rcu_state *rsp,
+ struct rcu_node *rnp,
+ struct rcu_data *rdp);
+static void rcu_preempt_offline_cpu(int cpu);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-static void __rcu_process_callbacks(struct rcu_state *rsp,
- struct rcu_data *rdp);
-static void __call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *rcu),
- struct rcu_state *rsp);
-static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp);
-static void __cpuinit rcu_init_percpu_data(int cpu, struct rcu_state *rsp,
- int preemptable);
+static void rcu_preempt_check_callbacks(int cpu);
+static void rcu_preempt_process_callbacks(void);
+void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
+static int rcu_preempt_pending(int cpu);
+static int rcu_preempt_needs_cpu(int cpu);
+static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
+static void __init __rcu_init_preempt(void);

-#include "rcutree_plugin.h"

/*
* Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
@@ -377,7 +382,7 @@ static long dyntick_recall_completed(struct rcu_state *rsp)
/*
* Snapshot the specified CPU's dynticks counter so that we can later
* credit them with an implicit quiescent state. Return 1 if this CPU
- * is already in a quiescent state courtesy of dynticks idle mode.
+ * is in dynticks idle mode, which is an extended quiescent state.
*/
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
@@ -624,9 +629,15 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
note_new_gpnum(rsp, rdp);

/*
- * Because we are first, we know that all our callbacks will
- * be covered by this upcoming grace period, even the ones
- * that were registered arbitrarily recently.
+ * Because this CPU just now started the new grace period, we know
+ * that all of its callbacks will be covered by this upcoming grace
+ * period, even the ones that were registered arbitrarily recently.
+ * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
+ *
+ * Other CPUs cannot be sure exactly when the grace period started.
+ * Therefore, their recently registered callbacks must pass through
+ * an additional RCU_NEXT_READY stage, so that they will be handled
+ * by the next RCU grace period.
*/
rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
@@ -886,7 +897,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)

/*
* Move callbacks from the outgoing CPU to the running CPU.
- * Note that the outgoing CPU is now quiscent, so it is now
+ * Note that the outgoing CPU is now quiescent, so it is now
* (uncharacteristically) safe to access its rcu_data structure.
* Note also that we must carefully retain the order of the
* outgoing CPU's callbacks in order for rcu_barrier() to work
@@ -1577,25 +1588,6 @@ do { \
} \
} while (0)

-#ifdef CONFIG_TREE_PREEMPT_RCU
-
-void __init __rcu_init_preempt(void)
-{
- int i; /* All used by RCU_INIT_FLAVOR(). */
- int j;
- struct rcu_node *rnp;
-
- RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);
-}
-
-#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
-
-void __init __rcu_init_preempt(void)
-{
-}
-
-#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
-
void __init __rcu_init(void)
{
int i; /* All used by RCU_INIT_FLAVOR(). */
@@ -1612,6 +1604,8 @@ void __init __rcu_init(void)
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
}

+#include "rcutree_plugin.h"
+
module_param(blimit, int, 0);
module_param(qhimark, int, 0);
module_param(qlowmark, int, 0);
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 9aa8c8a..a48d11f 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -79,15 +79,21 @@ struct rcu_dynticks {
* Definition for node within the RCU grace-period-detection hierarchy.
*/
struct rcu_node {
- spinlock_t lock;
+ spinlock_t lock; /* Root rcu_node's lock protects some */
+ /* rcu_state fields as well as following. */
long gpnum; /* Current grace period for this node. */
/* This will either be equal to or one */
/* behind the root rcu_node's gpnum. */
unsigned long qsmask; /* CPUs or groups that need to switch in */
/* order for current grace period to proceed.*/
+ /* In leaf rcu_node, each bit corresponds to */
+ /* an rcu_data structure, otherwise, each */
+ /* bit corresponds to a child rcu_node */
+ /* structure. */
unsigned long qsmaskinit;
/* Per-GP initialization for qsmask. */
unsigned long grpmask; /* Mask to apply to parent qsmask. */
+ /* Only one bit will be set in this mask. */
int grplo; /* lowest-numbered CPU or group here. */
int grphi; /* highest-numbered CPU or group here. */
u8 grpnum; /* CPU/group number for next level up. */
@@ -95,6 +101,9 @@ struct rcu_node {
struct rcu_node *parent;
struct list_head blocked_tasks[2];
/* Tasks blocked in RCU read-side critsect. */
+ /* Grace period number (->gpnum) x blocked */
+ /* by tasks on the (x & 0x1) element of the */
+ /* blocked_tasks[] array. */
} ____cacheline_internodealigned_in_smp;

/* Index values for nxttail array in struct rcu_data. */
@@ -126,19 +135,22 @@ struct rcu_data {
* Any of the partitions might be empty, in which case the
* pointer to that partition will be equal to the pointer for
* the following partition. When the list is empty, all of
- * the nxttail elements point to nxtlist, which is NULL.
+ * the nxttail elements point to the ->nxtlist pointer itself,
+ * which in that case is NULL.
*
- * [*nxttail[RCU_NEXT_READY_TAIL], NULL = *nxttail[RCU_NEXT_TAIL]):
- * Entries that might have arrived after current GP ended
- * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
- * Entries known to have arrived before current GP ended
- * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
- * Entries that batch # <= ->completed - 1: waiting for current GP
* [nxtlist, *nxttail[RCU_DONE_TAIL]):
* Entries that batch # <= ->completed
* The grace period for these entries has completed, and
* the other grace-period-completed entries may be moved
* here temporarily in rcu_process_callbacks().
+ * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
+ * Entries that batch # <= ->completed - 1: waiting for current GP
+ * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
+ * Entries known to have arrived before current GP ended
+ * [*nxttail[RCU_NEXT_READY_TAIL], *nxttail[RCU_NEXT_TAIL]):
+ * Entries that might have arrived after current GP ended
+ * Note that the value of *nxttail[RCU_NEXT_TAIL] will
+ * always be NULL, as this is the end of the list.
*/
struct rcu_head *nxtlist;
struct rcu_head **nxttail[RCU_NEXT_SIZE];
@@ -216,6 +228,9 @@ struct rcu_state {
/* Force QS state. */
long gpnum; /* Current gp number. */
long completed; /* # of last completed gp. */
+
+ /* End of fields guarded by root rcu_node's lock. */
+
spinlock_t onofflock; /* exclude on/offline and */
/* starting new GP. */
spinlock_t fqslock; /* Only one task forcing */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 8ff1ba7..6525021 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -419,6 +419,18 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
}

/*
+ * Initialize preemptable RCU's state structures.
+ */
+static void __init __rcu_init_preempt(void)
+{
+ int i; /* All used by RCU_INIT_FLAVOR(). */
+ int j;
+ struct rcu_node *rnp;
+
+ RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);
+}
+
+/*
* Check for a task exiting while in a preemptable-RCU read-side
* critical section, clean up if so. No need to issue warnings,
* as debug_check_no_locks_held() already does this if lockdep
@@ -518,7 +530,7 @@ static void rcu_preempt_offline_cpu(int cpu)
* Because preemptable RCU does not exist, it never has any callbacks
* to check.
*/
-void rcu_preempt_check_callbacks(int cpu)
+static void rcu_preempt_check_callbacks(int cpu)
{
}

@@ -526,7 +538,7 @@ void rcu_preempt_check_callbacks(int cpu)
* Because preemptable RCU does not exist, it never has any callbacks
* to process.
*/
-void rcu_preempt_process_callbacks(void)
+static void rcu_preempt_process_callbacks(void)
{
}

@@ -563,4 +575,11 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
{
}

+/*
+ * Because preemptable RCU does not exist, it need not be initialized.
+ */
+static void __init __rcu_init_preempt(void)
+{
+}
+
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */

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