ftrace: Revert 8ab2b7efd ftrace: Remove unnecessary disabling of irqs

Revert the commit that removed the disabling of interrupts around
the initial modifying of mcount callers to nops, and update the comment.

The original comment was outdated and stated that the interrupts were
being disabled to prevent kstop machine, which was required with the
old ftrace daemon, but was no longer the case.

What the comment failed to mention was that interrupts needed to be
disabled to keep interrupts from preempting the modifying of the code
and then executing the code that was partially modified.

Revert the commit and update the comment.

Reported-by: Richard W.M. Jones <rjones@redhat.com>
Tested-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 204b3eb4e690e4d31042c979d2f7da5eb4738577..908038f57440e5eec44233351578105ff8c64e08 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3330,6 +3330,7 @@ static int ftrace_process_locs(struct module *mod,
 {
        unsigned long *p;
        unsigned long addr;
+       unsigned long flags;
 
        mutex_lock(&ftrace_lock);
        p = start;
@@ -3346,7 +3347,13 @@ static int ftrace_process_locs(struct module *mod,
                ftrace_record_ip(addr);
        }
 
+       /*
+        * Disable interrupts to prevent interrupts from executing
+        * code that is being modified.
+        */
+       local_irq_save(flags);
        ftrace_update_code(mod);
+       local_irq_restore(flags);
        mutex_unlock(&ftrace_lock);
 
        return 0;