powerpc/kprobes: Pause function_graph tracing during jprobes handling

This fixes a crash when function_graph and jprobes are used together.
This is essentially commit 237d28db036e ("ftrace/jprobes/x86: Fix
conflict between jprobes and function graph tracing"), but for powerpc.

Jprobes breaks function_graph tracing since the jprobe hook needs to use
jprobe_return(), which never returns back to the hook, but instead to
the original jprobe'd function. The solution is to momentarily pause
function_graph tracing before invoking the jprobe hook and re-enable it
when returning back to the original jprobe'd function.

Fixes: 6794c78243bf ("powerpc64: port of the function graph tracer")
Cc: stable@vger.kernel.org # v2.6.30+
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index fc4343514bed..5075a4d6f1d7 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -617,6 +617,15 @@ int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 #endif
 
+        /*
+         * jprobes use jprobe_return() which skips the normal return
+         * path of the function, and this messes up the accounting of the
+         * function graph tracer.
+         *
+         * Pause function graph tracing while performing the jprobe function.
+         */
+        pause_graph_tracing();
+
         return 1;
 }
 NOKPROBE_SYMBOL(setjmp_pre_handler);
@@ -642,6 +651,8 @@ int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
          * saved regs...
          */
         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
+        /* It's OK to start function graph tracing again */
+        unpause_graph_tracing();
         preempt_enable_no_resched();
         return 1;
 }