ftrace: warn on failure to disable mcount callers

With the recent updates to ftrace, there should not be any failures when
modifying the code. If there is, then we need to warn about it.

This patch has a cleaned up version of the code that I used to discover
that the weak symbols were causing failures.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7694f3e597976ed77d0428666e1f01ffe82bbcaa..4dda4f60a2a9262770e3195b894e48b8178296a3 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -576,6 +576,16 @@ static void ftrace_shutdown_replenish(void)
        ftrace_pages->next = (void *)get_zeroed_page(GFP_KERNEL);
 }
 
+static void print_ip_ins(const char *fmt, unsigned char *p)
+{
+       int i;
+
+       printk(KERN_CONT "%s", fmt);
+
+       for (i = 0; i < MCOUNT_INSN_SIZE; i++)
+               printk(KERN_CONT "%s%02x", i ? ":" : "", p[i]);
+}
+
 static int
 ftrace_code_disable(struct dyn_ftrace *rec)
 {
@@ -590,6 +600,23 @@ ftrace_code_disable(struct dyn_ftrace *rec)
 
        failed = ftrace_modify_code(ip, call, nop);
        if (failed) {
+               switch (failed) {
+               case 1:
+                       WARN_ON_ONCE(1);
+                       pr_info("ftrace faulted on modifying ");
+                       print_ip_sym(ip);
+                       break;
+               case 2:
+                       WARN_ON_ONCE(1);
+                       pr_info("ftrace failed to modify ");
+                       print_ip_sym(ip);
+                       print_ip_ins(" expected: ", call);
+                       print_ip_ins(" actual: ", (unsigned char *)ip);
+                       print_ip_ins(" replace: ", nop);
+                       printk(KERN_CONT "\n");
+                       break;
+               }
+
                rec->flags |= FTRACE_FL_FAILED;
                return 0;
        }