[S390] kprobes breaks BUG_ON

The illegal operation handler calls the die notifier with DIE_BPT to
let kprobes pick up its breakpoint. If kprobes does not find its
breakpoint it returns NOTIFY_STOP instead of NOTIFY_DONE.
Since we use stop_machine_run on s390 to arm/disarm the kprobes
breakpoints the race that kprobe_handler tries to solve by checking
for the kprobes breakpoints does not exist. Removing the check makes
BUG_ON working again.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index a466bab6677e15f506da1fb3d8168d5792170167..8af549e95730970ad3ed67a43ab823bf420cf24d 100644 (file)
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -337,21 +337,14 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
        }
 
        p = get_kprobe(addr);
-       if (!p) {
-               if (*addr != BREAKPOINT_INSTRUCTION) {
-                       /*
-                        * The breakpoint instruction was removed right
-                        * after we hit it.  Another cpu has removed
-                        * either a probepoint or a debugger breakpoint
-                        * at this address.  In either case, no further
-                        * handling of this interrupt is appropriate.
-                        *
-                        */
-                       ret = 1;
-               }
-               /* Not one of ours: let kernel handle it */
+       if (!p)
+               /*
+                * No kprobe at this address. The fault has not been
+                * caused by a kprobe breakpoint. The race of breakpoint
+                * vs. kprobe remove does not exist because on s390 we
+                * use stop_machine_run to arm/disarm the breakpoints.
+                */
                goto no_kprobe;
-       }
 
        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
        set_current_kprobe(p, regs, kcb);