linux-kernel - [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all

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Date:   Wed, 05 Dec 2018 12:48:54 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     catalin.marinas@....com, will.deacon@....com,
        keescook@...omium.org, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org,
        Anders Roxell <anders.roxell@...aro.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all_code()

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

It has been reported that ftrace_replace_code() which is called by
ftrace_modify_all_code() can cause a soft lockup warning for an
allmodconfig kernel. This is because all the debug options enabled
causes the loop in ftrace_replace_code() (which loops over all the
functions being enabled where there can be 10s of thousands), is too
slow, and never schedules out.

To solve this, setting FTRACE_SCHEDULABLE to the command passed into
ftrace_replace_code() will make it call cond_resched() in the loop,
which prevents the soft lockup warning from triggering.

Link: http://lkml.kernel.org/r/20181204192903.8193-1-anders.roxell@linaro.org

Reported-by: Anders Roxell <anders.roxell@...aro.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 arch/arm64/kernel/ftrace.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 57e962290df3..9a8de0a79f97 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -193,6 +193,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,

 void arch_ftrace_update_code(int command)
 {
+	command |= FTRACE_SCHEDULABLE;
 	ftrace_modify_all_code(command);
 }

-- 
2.19.1