rcu: Add const annotation to char * for RCU tracepoints and functions

All the RCU tracepoints and functions that reference char pointers do
so with just 'char *' even though they do not modify the contents of
the string itself. This will cause warnings if a const char * is used
in one of these functions.

The RCU tracepoints store the pointer to the string to refer back to them
when the trace output is displayed. As this can be minutes, hours or
even days later, those strings had better be constant.

This change also opens the door to allow the RCU tracepoint strings and
their addresses to be exported so that userspace tracing tools can
translate the contents of the pointers of the RCU tracepoints.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

7 files changed, 11 insertions, 11 deletions

diff --git a/kernel/rcu.h b/kernel/rcu.h
index 7f8e7590e3e5..0a90ccc65bfb 100644
--- a/kernel/rcu.h
+++ b/kernel/rcu.h
@@ -94,7 +94,7 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
 
 extern void kfree(const void *);
 
-static inline bool __rcu_reclaim(char *rn, struct rcu_head *head)
+static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 {
         unsigned long offset = (unsigned long)head->func;
 
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index cce6ba8bbace..14994d4e1a54 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -377,7 +377,7 @@ EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
-void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp,
+void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
                                unsigned long secs,
                                unsigned long c_old, unsigned long c)
 {
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index aa344111de3e..9ed6075dc562 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -264,7 +264,7 @@ void rcu_check_callbacks(int cpu, int user)
  */
 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 {
-        char *rn = NULL;
+        const char *rn = NULL;
         struct rcu_head *next, *list;
         unsigned long flags;
         RCU_TRACE(int cb_count = 0);
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 0cd385acccfa..280d06cae352 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -36,7 +36,7 @@ struct rcu_ctrlblk {
         RCU_TRACE(unsigned long gp_start); /* Start time for stalls. */
         RCU_TRACE(unsigned long ticks_this_gp); /* Statistic for stalls. */
         RCU_TRACE(unsigned long jiffies_stall); /* Jiffies at next stall. */
-        RCU_TRACE(char *name);          /* Name of RCU type. */
+        RCU_TRACE(const char *name);    /* Name of RCU type. */
 };
 
 /* Definition for rcupdate control block. */
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index f4871e52c546..3d936f0fbcd8 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -267,7 +267,7 @@ rcutorture_shutdown_notify(struct notifier_block *unused1,
  * Absorb kthreads into a kernel function that won't return, so that
  * they won't ever access module text or data again.
  */
-static void rcutorture_shutdown_absorb(char *title)
+static void rcutorture_shutdown_absorb(const char *title)
 {
         if (ACCESS_ONCE(fullstop) == FULLSTOP_SHUTDOWN) {
                 pr_notice(
@@ -337,7 +337,7 @@ rcu_random(struct rcu_random_state *rrsp)
 }
 
 static void
-rcu_stutter_wait(char *title)
+rcu_stutter_wait(const char *title)
 {
         while (stutter_pause_test || !rcutorture_runnable) {
                 if (rcutorture_runnable)
@@ -366,7 +366,7 @@ struct rcu_torture_ops {
         int (*stats)(char *page);
         int irq_capable;
         int can_boost;
-        char *name;
+        const char *name;
 };
 
 static struct rcu_torture_ops *cur_ops;
@@ -1364,7 +1364,7 @@ rcu_torture_stutter(void *arg)
 }
 
 static inline void
-rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag)
+rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
 {
         pr_alert("%s" TORTURE_FLAG
                  "--- %s: nreaders=%d nfakewriters=%d "
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 068de3a93606..30201494560b 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1032,7 +1032,7 @@ static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
  * rcu_nocb_wait_gp().
  */
 static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
-                                unsigned long c, char *s)
+                                unsigned long c, const char *s)
 {
         trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
                                       rnp->completed, c, rnp->level,
@@ -2720,7 +2720,7 @@ static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
  * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
  * the compiler is expected to optimize this away.
  */
-static void _rcu_barrier_trace(struct rcu_state *rsp, char *s,
+static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
                                int cpu, unsigned long done)
 {
         trace_rcu_barrier(rsp->name, s, cpu,
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index b3832581043c..cbdeac6cea9e 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -445,7 +445,7 @@ struct rcu_state {
                                                 /*  for CPU stalls. */
         unsigned long gp_max;                   /* Maximum GP duration in */
                                                 /*  jiffies. */
-        char *name;                             /* Name of structure. */
+        const char *name;                       /* Name of structure. */
         char abbr;                              /* Abbreviated name. */
         struct list_head flavors;               /* List of RCU flavors. */
         struct irq_work wakeup_work;            /* Postponed wakeups */