When running in qemu on an kernel built with allmodconfig and debug options (in particular kcov and ubsan) enabled, ftrace_replace_code function call take minutes. The ftrace selftest calls ftrace_replace_code to look >40000 through ftrace_make_call/ftrace_make_nop, and these end up calling __aarch64_insn_write/aarch64_insn_patch_text_nosync.
Microseconds add up because this is called in a loop for each dyn_ftrace record, and this triggers the softlockup watchdog unless we let it sleep occasionally. Rework so that we call cond_resched() if !irqs_disabled() && !preempt_count(). Suggested-by: Steven Rostedt (VMware) <[email protected]> Signed-off-by: Anders Roxell <[email protected]> --- kernel/trace/ftrace.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index c375e33239f7..582e3441e318 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -2419,11 +2419,14 @@ void __weak ftrace_replace_code(int enable) { struct dyn_ftrace *rec; struct ftrace_page *pg; + bool schedulable; int failed; if (unlikely(ftrace_disabled)) return; + schedulable = !irqs_disabled() && !preempt_count(); + do_for_each_ftrace_rec(pg, rec) { if (rec->flags & FTRACE_FL_DISABLED) @@ -2435,6 +2438,13 @@ void __weak ftrace_replace_code(int enable) /* Stop processing */ return; } + /* + * Some archs calls this function with interrupts or preemption + * disabled. Howeve, other archs don't and this can cause a + * tremendous unneeded latency. + */ + if (schedulable) + cond_resched(); } while_for_each_ftrace_rec(); } -- 2.19.2
