linux-kernel - [PATCH] kprobes: Fix to delay the kprobes jump optimization

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Message-Id: <161365856280.719838.12423085451287256713.stgit@devnote2>
Date:   Thu, 18 Feb 2021 23:29:23 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Uladzislau Rezki <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Axtens <dja@...ens.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Michal Hocko <mhocko@...e.com>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: [PATCH] kprobes: Fix to delay the kprobes jump optimization

Commit 36dadef23fcc ("kprobes: Init kprobes in early_initcall")
moved the kprobe setup in early_initcall(), which includes kprobe
jump optimization.
The kprobes jump optimizer involves synchronize_rcu_tasks() which
depends on the ksoftirqd and rcu_spawn_tasks_*(). However, since
those are setup in core_initcall(), kprobes jump optimizer can not
run at the early_initcall().

To avoid this issue, make the kprobe optimization disabled in the
early_initcall() and enables it in subsys_initcall().

Note that non-optimized kprobes is still available after
early_initcall(). Only jump optimization is delayed.

Fixes: 36dadef23fcc ("kprobes: Init kprobes in early_initcall")
Reported-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Cc: stable@...r.kernel.org
---
 kernel/kprobes.c |   31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index d5a3eb74a657..779d8322e307 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -861,7 +861,6 @@ static void try_to_optimize_kprobe(struct kprobe *p)
 	cpus_read_unlock();
 }
 
-#ifdef CONFIG_SYSCTL
 static void optimize_all_kprobes(void)
 {
 	struct hlist_head *head;
@@ -887,6 +886,7 @@ static void optimize_all_kprobes(void)
 	mutex_unlock(&kprobe_mutex);
 }
 
+#ifdef CONFIG_SYSCTL
 static void unoptimize_all_kprobes(void)
 {
 	struct hlist_head *head;
@@ -2497,18 +2497,14 @@ static int __init init_kprobes(void)
 		}
 	}
 
-#if defined(CONFIG_OPTPROBES)
-#if defined(__ARCH_WANT_KPROBES_INSN_SLOT)
-	/* Init kprobe_optinsn_slots */
-	kprobe_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
-#endif
-	/* By default, kprobes can be optimized */
-	kprobes_allow_optimization = true;
-#endif
-
 	/* By default, kprobes are armed */
 	kprobes_all_disarmed = false;
 
+#if defined(CONFIG_OPTPROBES) && defined(__ARCH_WANT_KPROBES_INSN_SLOT)
+	/* Init kprobe_optinsn_slots for allocation */
+	kprobe_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
+#endif
+
 	err = arch_init_kprobes();
 	if (!err)
 		err = register_die_notifier(&kprobe_exceptions_nb);
@@ -2523,6 +2519,21 @@ static int __init init_kprobes(void)
 }
 early_initcall(init_kprobes);
 
+#if defined(CONFIG_OPTPROBES)
+static int __init init_optprobes(void)
+{
+	/*
+	 * Enable kprobe optimization - this kicks the optimizer which
+	 * depends on synchronize_rcu_tasks() and ksoftirqd, that is
+	 * not spawned in early initcall. So delay the optimization.
+	 */
+	optimize_all_kprobes();
+
+	return 0;
+}
+subsys_initcall(init_optprobes);
+#endif
+
 #ifdef CONFIG_DEBUG_FS
 static void report_probe(struct seq_file *pi, struct kprobe *p,
 		const char *sym, int offset, char *modname, struct kprobe *pp)