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

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Date:	Mon, 17 Feb 2014 16:22:52 +0100
From:	Petr Mladek <pmladek@...e.cz>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jiri Kosina <jkosina@...e.cz>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Petr Mladek <pmladek@...e.cz>
Subject: [PATCH 3/4] x86: BUG when ftrace patching recovery fails

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@...e.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

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