powerpc, hw_breakpoint: Cooperate better with other single-steppers

The code we had to clear the MSR_SE bit was not doing anything because
the caller (ultimately single_step_exception() in traps.c) had already
cleared.  Instead of trying to leave MSR_SE set if the TIF_SINGLESTEP
flag is set (which indicates that the process is being single-stepped
by ptrace), we instead return NOTIFY_DONE in that case, which means
the caller will generate a SIGTRAP for the process.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index 241e09712314..5a1d55d06a08 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -304,15 +304,16 @@ int __kprobes single_step_dabr_instruction(struct die_args *args)
         if (!bp_info->extraneous_interrupt)
                 perf_bp_event(bp, regs);
 
+        set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION);
+        current->thread.last_hit_ubp = NULL;
+
         /*
-         * Do not disable MSR_SE if the process was already in
-         * single-stepping mode.
+         * If the process was being single-stepped by ptrace, let the
+         * other single-step actions occur (e.g. generate SIGTRAP).
          */
-        if (!test_thread_flag(TIF_SINGLESTEP))
-                regs->msr &= ~MSR_SE;
+        if (test_thread_flag(TIF_SINGLESTEP))
+                return NOTIFY_DONE;
 
-        set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION);
-        current->thread.last_hit_ubp = NULL;
         return NOTIFY_STOP;
 }