[PATCH v3] tracing: add cond_resched to ftrace_replace_code()
From: Anders Roxell
Date: Tue Dec 04 2018 - 14:40:56 EST
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) <rostedt@xxxxxxxxxxx>
Signed-off-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
---
kernel/trace/ftrace.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index c375e33239f7..7c9f49a5a1ab 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2419,11 +2419,19 @@ void __weak ftrace_replace_code(int enable)
{
struct dyn_ftrace *rec;
struct ftrace_page *pg;
+ bool schedulable;
int failed;
if (unlikely(ftrace_disabled))
return;
+ /*
+ * Some archs call this function with interrupts or preemption
+ * disabled. However, for other archs that can preempt, this can cause
+ * an tremendous unneeded latency.
+ */
+ schedulable = !irqs_disabled() && !preempt_count();
+
do_for_each_ftrace_rec(pg, rec) {
if (rec->flags & FTRACE_FL_DISABLED)
@@ -2435,6 +2443,8 @@ void __weak ftrace_replace_code(int enable)
/* Stop processing */
return;
}
+ if (schedulable)
+ cond_resched();
} while_for_each_ftrace_rec();
}
--
2.19.2