Re: [RFC PATCH bpf-next v3 1/2] ftrace: deprecate disabling via ftrace_enabled sysctl

On Thu, Aug 6, 2026 at 5:52 PM Andrey Grodzovsky
[off-list ref] wrote:

On Thu, Aug 6, 2026 at 5:22 PM Song Liu [off-list ref] wrote:

quoted

On Thu, Aug 6, 2026 at 8:30 AM Andrey Grodzovsky
[off-list ref] wrote:

quoted

Writing 0 to kernel.ftrace_enabled has not reliably disabled ftrace
for years (FTRACE_OPS_FL_PERMANENT users already block it, and more
callers rely on ftrace always being on). Refuse the write instead of
leaving it in an inconsistent "disables some, not all" state: return
-EOPNOTSUPP and log a message. Reads and enabling (writing 1) are
unaffected.

Update the docs to note the deprecation up front.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrey Grodzovsky <redacted>

Sashiko's comments make sense. Other than those:

The bot has 2 comments.

In my opinion, the test-breaking comment is wrong as he looked
strictly at this patch w/o reviewing the follow-up live patch testing
changes which update the tests to avoid breaks.

The cleanup comment is valid but since we aren't sure if we'll need to
revert this change later if it breaks userspace in some unseen way, I
wonder how extensive the cleanup should be? Steven, can you advise
please ?

Andrey

Gentle ping on this question above Steven.

Andrey

quoted

Acked-by: Song Liu <song@kernel.org>

quoted

---
 Documentation/trace/ftrace.rst |  5 ++++
 kernel/trace/ftrace.c          | 43 +++++-----------------------------
 2 files changed, 11 insertions(+), 37 deletions(-)