On Thu, 13 Jun 2024 13:29:58 +0530 Naresh Kamboju naresh.kamboju@linaro.org wrote:
--- a/kernel/trace/fgraph.c +++ b/kernel/trace/fgraph.c @@ -641,7 +641,7 @@ int function_graph_enter(unsigned long ret, unsigned long func, { for_each_set_bit(i, &fgraph_array_bitmask, sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
struct fgraph_ops *gops = fgraph_array[i];
struct fgraph_ops *gops = READ_ONCE(fgraph_array[i]); int save_curr_ret_stack; if (gops == &fgraph_stub)Because if the compiler decides to re-read gops from fgraph_array[i] after the above check for the following line that does:
save_curr_ret_stack = current->curr_ret_stack; if (ftrace_ops_test(&gops->ops, func, NULL) && gops->entryfunc(&trace, gops)) bitmap |= BIT(i);and gops now points to fgraph_stub, it will trigger this bug.
Can you apply the above change and see if the bug goes away?
I will apply this patch and run the test in a loop. Since it is only seen once. Not sure I could validate this and confirm.
We could just look at the code that clang produced and see if it accesses the fgraph_array[] again. If this was the cause, it would show up it in the code.
But regardless, I think I'm going to add that READ_ONCE() anyway, because it is legitimate for the compiler to do the above without it.
Thanks,
-- Steve