[RFA][PATCH 1/5] ftrace/x86: Run a sync after fixup on failure

[Steven Rostedt <rostedt@goodmis.org>]

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[Request for Ack]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

If a failure occurs while enabling a trace, it bails out and will remove
the tracepoints to be back to what the code originally was. But the fix
up had some bugs in it. By injecting a failure in the code, the fix up
ran to completion, but shortly afterward the system rebooted.

There was two bugs here.

The first was that there was no final sync run across the CPUs after the
fix up was done, and before the ftrace int3 handler flag was reset. That
means that other CPUs could still see the breakpoint and trigger on it
long after the flag was cleared, and the int3 handler would think it was
a spurious interrupt. Worse yet, the int3 handler could hit other breakpoints
because the ftrace int3 handler flag would have prevented the int3 handler
from going further.

The second bug was that the removal of the breakpoints required the
"within()" logic updates instead of accessing the ip address directly.

Link: http://lkml.kernel.org/r/1392650573-3390-1-git-send-email-pmladek@suse.cz

Reported-by: Petr Mladek <pmladek@suse.cz>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: stable@vger.kernel.org # 3.5+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 arch/x86/kernel/ftrace.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index e625319..6b566c8 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -455,7 +455,7 @@ static int remove_breakpoint(struct dyn_ftrace *rec)
 	}
 
  update:
-	return probe_kernel_write((void *)ip, &nop[0], 1);
+	return ftrace_write(ip, nop, 1);
 }
 
 static int add_update_code(unsigned long ip, unsigned const char *new)
@@ -634,6 +634,7 @@ void ftrace_replace_code(int enable)
 		rec = ftrace_rec_iter_record(iter);
 		remove_breakpoint(rec);
 	}
+	run_sync();
 }
 
 static int
@@ -664,7 +665,7 @@ ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
 	return ret;
 
  fail_update:
-	probe_kernel_write((void *)ip, &old_code[0], 1);
+	ftrace_write(ip, old_code, 1);
 	goto out;
 }
 
-- 
1.8.5.3