3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Torvalds <torva...@linux-foundation.org>

commit f67b15037a7a50c57f72e69a6d59941ad90a0f0f upstream.

Annoyingly, modify_user_hw_breakpoint() unnecessarily complicates the
modification of a breakpoint - simplify it and remove the pointless
local variables.

Also update the stale Docbook while at it.

Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Acked-by: Thomas Gleixner <t...@linutronix.de>
Cc: <sta...@vger.kernel.org>
Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Jiri Olsa <jo...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Stephane Eranian <eran...@google.com>
Cc: Vince Weaver <vincent.wea...@maine.edu>
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 kernel/events/hw_breakpoint.c |   30 +++++++-----------------------
 1 file changed, 7 insertions(+), 23 deletions(-)

--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -427,16 +427,9 @@ EXPORT_SYMBOL_GPL(register_user_hw_break
  * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
  * @bp: the breakpoint structure to modify
  * @attr: new breakpoint attributes
- * @triggered: callback to trigger when we hit the breakpoint
- * @tsk: pointer to 'task_struct' of the process to which the address belongs
  */
 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr 
*attr)
 {
-       u64 old_addr = bp->attr.bp_addr;
-       u64 old_len = bp->attr.bp_len;
-       int old_type = bp->attr.bp_type;
-       int err = 0;
-
        /*
         * modify_user_hw_breakpoint can be invoked with IRQs disabled and 
hence it
         * will not be possible to raise IPIs that invoke __perf_event_disable.
@@ -451,27 +444,18 @@ int modify_user_hw_breakpoint(struct per
        bp->attr.bp_addr = attr->bp_addr;
        bp->attr.bp_type = attr->bp_type;
        bp->attr.bp_len = attr->bp_len;
+       bp->attr.disabled = 1;
 
-       if (attr->disabled)
-               goto end;
-
-       err = validate_hw_breakpoint(bp);
-       if (!err)
-               perf_event_enable(bp);
+       if (!attr->disabled) {
+               int err = validate_hw_breakpoint(bp);
 
-       if (err) {
-               bp->attr.bp_addr = old_addr;
-               bp->attr.bp_type = old_type;
-               bp->attr.bp_len = old_len;
-               if (!bp->attr.disabled)
-                       perf_event_enable(bp);
+               if (err)
+                       return err;
 
-               return err;
+               perf_event_enable(bp);
+               bp->attr.disabled = 0;
        }
 
-end:
-       bp->attr.disabled = attr->disabled;
-
        return 0;
 }
 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);


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