Re: [for-linus v2][PATCH 0/2] ftrace: Fixes for v6.13

[Steven Rostedt]

On Tue, 17 Dec 2024 11:18:40 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> Ftrace fixes for 6.13:
> 
> - Always try to initialize the idle functions when graph tracer starts
> 
>   A bug was found that when a CPU is offline when graph tracing starts
>   and then comes online, that CPU is not traced. The fix to that was
>   to move the initialization of the idle shadow stack over to the
>   hot plug online logic, which also handle onlined CPUs. The issue was
>   that it removed the initialization of the shadow stack when graph tracing
>   starts, but the callbacks to the hot plug logic do nothing if graph
>   tracing isn't currently running. Although that fix fixed the onlining
>   of a CPU during tracing, it broke the CPUs that were already online.
> 
> - Have microblaze not try to get the "true parent" in function tracing
> 
>   If function tracing and graph tracing are both enabled at the same time
>   the parent of the functions traced by the function tracer may sometimes
>   be the graph tracing trampoline. The graph tracing hijacks the return
>   pointer of the function to trace it, but that can interfere with the
>   function tracing parent output. This was fixed by using the
>   ftrace_graph_ret_addr() function passing in the kernel stack pointer
>   using the ftrace_regs_get_stack_pointer() function. But Al Viro reported
>   that Microblaze does not implement the kernel_stack_pointer(regs)
>   helper function that ftrace_regs_get_stack_pointer() uses and fails
>   to compile when function graph tracing is enabled.
> 
>   It was first thought that this was a microblaze issue, but the real
>   cause is that this only works when an architecture implements
>   HAVE_DYNAMIC_FTRACE_WITH_ARGS, as a requirement for that config
>   is to have ftrace always pass a valid ftrace_regs to the callbacks.
>   That also means that the architecture supports ftrace_regs_get_stack_pointer()
>   Microblaze does not set HAVE_DYNAMIC_FTRACE_WITH_ARGS nor does it
>   implement ftrace_regs_get_stack_pointer() which caused it to fail to
>   build. Only implement the "true parent" logic if an architecture has
>   that config set.
> 
> Changes since v1: https://lore.kernel.org/all/20241214182138.4e7984a2@xxxxxxxxxxxxxxxxx/
> 
> - Removed the hash-ptr fix as Linus was unhappy with the code it was
>   fixing and I have another series to address that. It didn't even
>   belong in this pull request, as this is the ftrace topic and that
>   was a tracing topic.
> 
> - Properly fix the function_get_true_parent_ip(), which wasn't a
>   microblaze issue at all, but an issue for any architecture that
>   does not support HAVE_DYNAMIC_FTRACE_WITH_ARGS.


I forgot to append the diffstat and branch where this lives:

  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
ftrace/fixes

Head SHA1: 166438a432d76c68d3f0da60667248f3c2303d6c


Steven Rostedt (2):
      fgraph: Still initialize idle shadow stacks when starting
      ftrace: Do not find "true_parent" if HAVE_DYNAMIC_FTRACE_WITH_ARGS is not set

----
 kernel/trace/fgraph.c          | 8 +++++++-
 kernel/trace/trace_functions.c | 3 ++-
 2 files changed, 9 insertions(+), 2 deletions(-)