[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>

1 files changed, 7 insertions, 14 deletions

diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index a466bab6677e..8af549e95730 100644
--- 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);