On Mon, 18 Apr 2022 11:51:16 +0530 "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> > --- a/arch/powerpc/kernel/trace/ftrace.c > > +++ b/arch/powerpc/kernel/trace/ftrace.c > > @@ -78,10 +78,7 @@ ftrace_modify_code(unsigned long ip, ppc_inst_t old, > > ppc_inst_t new) > > } > > > > /* replace the text with the new text */ > > - if (patch_instruction((u32 *)ip, new)) > > - return -EPERM; > > - > > - return 0; > > + return patch_instruction((u32 *)ip, new); > > I think the reason we were returning -EPERM is so that ftrace_bug() can That is correct. > throw the right error message. That will change due to this patch, > though I'm not sure how much it matters. -EFAULT and -EPERM seem to > print almost the same error message. In these cases it helps to know the type of failure, as the way to debug it is different. -EFAULT: It failed to read it the location. This means that the memory is likely not even mapped in, or the pointer is way off. -EINVAL: Means that what was read did not match what was expected (the code was already updated, pointing to the wrong location, or simply the calculation of what to expect is incorrect). -EPERM: Means the write failed. What was read was expected, but the permissions to write have not been updated properly. Differentiating the three is crucial to looking at where the issue lies when an ftrace_bug() triggers. -- Steve
