powerpc/hw_breakpoints: Fix incorrect pointer access

If arch_validate_hwbkpt_settings() fails, bp->ctx won't be valid and the
kernel panics. Add a check to fix this.

Reported-by: Edjunior Barbosa Machado <emachado@linux.vnet.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index 2bc0584..f3a82dd 100644 (file)
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -111,7 +111,7 @@ void arch_unregister_hw_breakpoint(struct perf_event *bp)
         * and the single_step_dabr_instruction(), then cleanup the breakpoint
         * restoration variables to prevent dangling pointers.
         */
-       if (bp->ctx->task)
+       if (bp->ctx && bp->ctx->task)
                bp->ctx->task->thread.last_hit_ubp = NULL;
 }