rcutorture: Make cur_ops->format_gp_seqs take buffer length

The Tree and Tiny implementations of rcutorture_format_gp_seqs() use
hard-coded constants for the length of the buffer that they format into.
This is of course an accident waiting to happen, so this commit therefore
makes them take a length argument.  The rcutorture calling code uses
ARRAY_SIZE() to safely compute this new argument.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

Author: paulmckrcu

kernel/rcu/rcu.h

@@ -591,7 +591,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
 static inline void rcu_gp_set_torture_wait(int duration) { }
 #endif
 unsigned long long rcutorture_gather_gp_seqs(void);
-void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp);
+void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len);
 
 #ifdef CONFIG_TINY_SRCU
 

kernel/rcu/rcutorture.c

@@ -411,7 +411,7 @@ struct rcu_torture_ops {
 	void (*gp_slow_unregister)(atomic_t *rgssp);
 	bool (*reader_blocked)(void);
 	unsigned long long (*gather_gp_seqs)(void);
-	void (*format_gp_seqs)(unsigned long long seqs, char *cp);
+	void (*format_gp_seqs)(unsigned long long seqs, char *cp, size_t len);
 	long cbflood_max;
 	int irq_capable;
 	int can_boost;
@@ -3688,8 +3688,10 @@ rcu_torture_cleanup(void)
 				char buf2[20+1];
 				char sepchar = '-';
 
-				cur_ops->format_gp_seqs(err_segs[i].rt_gp_seq, buf1);
-				cur_ops->format_gp_seqs(err_segs[i].rt_gp_seq_end, buf2);
+				cur_ops->format_gp_seqs(err_segs[i].rt_gp_seq,
+							buf1, ARRAY_SIZE(buf1));
+				cur_ops->format_gp_seqs(err_segs[i].rt_gp_seq_end,
+							buf2, ARRAY_SIZE(buf2));
 				if (err_segs[i].rt_gp_seq == err_segs[i].rt_gp_seq_end) {
 					if (buf2[0]) {
 						for (j = 0; buf2[j]; j++)

kernel/rcu/tiny.c

@@ -264,9 +264,9 @@ unsigned long long rcutorture_gather_gp_seqs(void)
 }
 EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs);
 
-void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp)
+void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len)
 {
-	snprintf(cp, 8, "g%04llx", seqs & 0xffffULL);
+	snprintf(cp, len, "g%04llx", seqs & 0xffffULL);
 }
 EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs);
 #endif

kernel/rcu/tree.c

@@ -548,13 +548,13 @@ unsigned long long rcutorture_gather_gp_seqs(void)
 EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs);
 
 /* Format grace-period sequence numbers for rcutorture diagnostics. */
-void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp)
+void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len)
 {
 	unsigned int egp = (seqs >> 16) & 0xffffffULL;
 	unsigned int ggp = (seqs >> 40) & 0xffffULL;
 	unsigned int pgp = seqs & 0xffffULL;
 
-	snprintf(cp, 20, "g%04x:e%06x:p%04x", ggp, egp, pgp);
+	snprintf(cp, len, "g%04x:e%06x:p%04x", ggp, egp, pgp);
 }
 EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs);