[PATCH 3/4] x86: BUG when ftrace patching recovery fails

[Petr Mladek <pmladek@suse.cz>]

Ftrace modifies function calls using Int3 breakpoints on x86.
The breakpoints are handled only when the patching is in progress.
If something goes wrong, there is a recovery code that removes
the breakpoints. If this fails, the system might get silently
rebooted when a remaining break is not handled or an invalid
instruction is proceed.

A better solution is to BUG() when the recovery fails. It helps
to point to the sinner responsible for the reboot.

Signed-off-by: Petr Mladek <pmladek@suse.cz>
---
 arch/x86/kernel/ftrace.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 30d63c4a4195..525a9f954c8b 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -424,7 +424,7 @@ static int remove_breakpoint(struct dyn_ftrace *rec)
 
 	/* If this does not have a breakpoint, we are done */
 	if (ins[0] != BREAKPOINT_INSTRUCTION)
-		return -1;
+		return 0;
 
 	/* Check if it is nop instruction */
 	valid_ins = ftrace_nop_replace();
@@ -625,8 +625,15 @@ void ftrace_replace_code(int enable)
 	ftrace_bug(ret, rec ? rec->ip : 0);
 	printk(KERN_WARNING "Failed on %s (%d):\n", report, count);
 	for_ftrace_rec_iter(iter) {
+		int err;
+
 		rec = ftrace_rec_iter_record(iter);
-		remove_breakpoint(rec);
+		err = remove_breakpoint(rec);
+		/*
+		 * The breakpoints will not be handled after this function
+		 * finishes. Let's stop on a well defined point.
+		 */
+		BUG_ON(err);
 	}
 }
 
-- 
1.8.4