On Tue, 7 May 2024 23:09:22 +0900 "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote: > @@ -109,6 +244,21 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, > if (!current->ret_stack) > return -EBUSY; > > + /* > + * At first, check whether the previous fgraph callback is pushed by > + * the fgraph on the same function entry. > + * But if @func is the self tail-call function, we also need to ensure > + * the ret_stack is not for the previous call by checking whether the > + * bit of @fgraph_idx is set or not. > + */ > + ret_stack = get_ret_stack(current, current->curr_ret_stack, &offset); > + if (ret_stack && ret_stack->func == func && > + get_fgraph_type(current, offset + FGRAPH_FRAME_OFFSET) == FGRAPH_TYPE_BITMAP && > + !is_fgraph_index_set(current, offset + FGRAPH_FRAME_OFFSET, fgraph_idx)) > + return offset + FGRAPH_FRAME_OFFSET; > + > + val = (FGRAPH_TYPE_RESERVED << FGRAPH_TYPE_SHIFT) | FGRAPH_FRAME_OFFSET; > + > BUILD_BUG_ON(SHADOW_STACK_SIZE % sizeof(long)); I'm trying to figure out what the above is trying to do. This gets called once in function_graph_enter() (or function_graph_enter_ops()). What exactly are you trying to catch here? Is it from this email: https://lore.kernel.org/all/20231110105154.df937bf9f200a0c16806c522@xxxxxxxxxx/ As that's the last version before you added the above code. But you also noticed it may not be needed, but triggered a crash without it in v3: https://lore.kernel.org/all/20231205234511.3839128259dfec153ea7da81@xxxxxxxxxx/ I removed this code in my version and it runs just fine. Perhaps there was another bug that this was hiding that you fixed in later versions? -- Steve
