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Commit 2d1e38f5 authored by Thomas Gleixner's avatar Thomas Gleixner
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kprobes: Cure hotplug lock ordering issues 



Converting the cpu hotplug locking to a percpu rwsem unearthed hidden lock
ordering problems.

There is a wide range of locks involved in this: kprobe_mutex,
jump_label_mutex, ftrace_lock, text_mutex, event_mutex, module_mutex,
func_hash->regex_lock and a gazillion of lock order permutations with
nested get_online_cpus() calls.

Some of those permutations are potential deadlocks even with the current
nesting hotplug locking scheme, but they can't be discovered by lockdep.

The conversion of the hotplug locking to a percpu rwsem requires to prevent
nested locking, so it's required to take the hotplug rwsem early in the
call chain and establish a proper lock order.

After quite some analysis and going down the wrong road severa times the
following lock order has been chosen:

kprobe_mutex -> cpus_rwsem -> jump_label_mutex -> text_mutex

For kprobes which hook on an ftrace function trace point, it's required to
drop cpus_rwsem before calling into the ftrace code to avoid a deadlock on
the func_hash->regex_lock.

[ Steven: Ftrace interaction fixes ]

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Link: http://lkml.kernel.org/r/20170524081549.104864779@linutronix.de
parent f2545b2d

kernel/kprobes.c

+32 −27
Original line number Diff line number Diff line
@@ -483,11 +483,6 @@ static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer); 
 */

static void do_optimize_kprobes(void)

{

	/* Optimization never be done when disarmed */

	if (kprobes_all_disarmed || !kprobes_allow_optimization ||

	    list_empty(&optimizing_list))

		return;



	/*

	 * The optimization/unoptimization refers online_cpus via

	 * stop_machine() and cpu-hotplug modifies online_cpus.
@@ -495,14 +490,19 @@ static void do_optimize_kprobes(void) 
	 * This combination can cause a deadlock (cpu-hotplug try to lock

	 * text_mutex but stop_machine can not be done because online_cpus

	 * has been changed)

	 * To avoid this deadlock, we need to call get_online_cpus()

	 * To avoid this deadlock, caller must have locked cpu hotplug

	 * for preventing cpu-hotplug outside of text_mutex locking.

	 */

	get_online_cpus();

	lockdep_assert_cpus_held();



	/* Optimization never be done when disarmed */

	if (kprobes_all_disarmed || !kprobes_allow_optimization ||

	    list_empty(&optimizing_list))

		return;



	mutex_lock(&text_mutex);

	arch_optimize_kprobes(&optimizing_list);

	mutex_unlock(&text_mutex);

	put_online_cpus();

}



/*
@@ -513,12 +513,13 @@ static void do_unoptimize_kprobes(void) 
{

	struct optimized_kprobe *op, *tmp;



	/* See comment in do_optimize_kprobes() */

	lockdep_assert_cpus_held();



	/* Unoptimization must be done anytime */

	if (list_empty(&unoptimizing_list))

		return;



	/* Ditto to do_optimize_kprobes */

	get_online_cpus();

	mutex_lock(&text_mutex);

	arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);

	/* Loop free_list for disarming */
@@ -537,7 +538,6 @@ static void do_unoptimize_kprobes(void) 
			list_del_init(&op->list);

	}

	mutex_unlock(&text_mutex);

	put_online_cpus();

}



/* Reclaim all kprobes on the free_list */
@@ -562,6 +562,7 @@ static void kick_kprobe_optimizer(void) 
static void kprobe_optimizer(struct work_struct *work)

{

	mutex_lock(&kprobe_mutex);

	cpus_read_lock();

	/* Lock modules while optimizing kprobes */

	mutex_lock(&module_mutex);
@@ -587,6 +588,7 @@ static void kprobe_optimizer(struct work_struct *work) 
	do_free_cleaned_kprobes();



	mutex_unlock(&module_mutex);

	cpus_read_unlock();

	mutex_unlock(&kprobe_mutex);



	/* Step 5: Kick optimizer again if needed */
@@ -650,9 +652,8 @@ static void optimize_kprobe(struct kprobe *p) 
/* Short cut to direct unoptimizing */

static void force_unoptimize_kprobe(struct optimized_kprobe *op)

{

	get_online_cpus();

	lockdep_assert_cpus_held();

	arch_unoptimize_kprobe(op);

	put_online_cpus();

	if (kprobe_disabled(&op->kp))

		arch_disarm_kprobe(&op->kp);

}
@@ -791,6 +792,7 @@ static void try_to_optimize_kprobe(struct kprobe *p) 
		return;



	/* For preparing optimization, jump_label_text_reserved() is called */

	cpus_read_lock();

	jump_label_lock();

	mutex_lock(&text_mutex);
@@ -812,6 +814,7 @@ static void try_to_optimize_kprobe(struct kprobe *p) 
out:

	mutex_unlock(&text_mutex);

	jump_label_unlock();

	cpus_read_unlock();

}



#ifdef CONFIG_SYSCTL
@@ -826,6 +829,7 @@ static void optimize_all_kprobes(void) 
	if (kprobes_allow_optimization)

		goto out;



	cpus_read_lock();

	kprobes_allow_optimization = true;

	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {

		head = &kprobe_table[i];
@@ -833,6 +837,7 @@ static void optimize_all_kprobes(void) 
			if (!kprobe_disabled(p))

				optimize_kprobe(p);

	}

	cpus_read_unlock();

	printk(KERN_INFO "Kprobes globally optimized\n");

out:

	mutex_unlock(&kprobe_mutex);
@@ -851,6 +856,7 @@ static void unoptimize_all_kprobes(void) 
		return;

	}



	cpus_read_lock();

	kprobes_allow_optimization = false;

	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {

		head = &kprobe_table[i];
@@ -859,6 +865,7 @@ static void unoptimize_all_kprobes(void) 
				unoptimize_kprobe(p, false);

		}

	}

	cpus_read_unlock();

	mutex_unlock(&kprobe_mutex);



	/* Wait for unoptimizing completion */
@@ -1010,14 +1017,11 @@ static void arm_kprobe(struct kprobe *kp) 
		arm_kprobe_ftrace(kp);

		return;

	}

	/*

	 * Here, since __arm_kprobe() doesn't use stop_machine(),

	 * this doesn't cause deadlock on text_mutex. So, we don't

	 * need get_online_cpus().

	 */

	cpus_read_lock();

	mutex_lock(&text_mutex);

	__arm_kprobe(kp);

	mutex_unlock(&text_mutex);

	cpus_read_unlock();

}



/* Disarm a kprobe with text_mutex */
@@ -1027,10 +1031,12 @@ static void disarm_kprobe(struct kprobe *kp, bool reopt) 
		disarm_kprobe_ftrace(kp);

		return;

	}

	/* Ditto */



	cpus_read_lock();

	mutex_lock(&text_mutex);

	__disarm_kprobe(kp, reopt);

	mutex_unlock(&text_mutex);

	cpus_read_unlock();

}



/*
@@ -1298,13 +1304,10 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p) 
	int ret = 0;

	struct kprobe *ap = orig_p;



	cpus_read_lock();



	/* For preparing optimization, jump_label_text_reserved() is called */

	jump_label_lock();

	/*

	 * Get online CPUs to avoid text_mutex deadlock.with stop machine,

	 * which is invoked by unoptimize_kprobe() in add_new_kprobe()

	 */

	get_online_cpus();

	mutex_lock(&text_mutex);



	if (!kprobe_aggrprobe(orig_p)) {
@@ -1352,8 +1355,8 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p) 


out:

	mutex_unlock(&text_mutex);

	put_online_cpus();

	jump_label_unlock();

	cpus_read_unlock();



	if (ret == 0 && kprobe_disabled(ap) && !kprobe_disabled(p)) {

		ap->flags &= ~KPROBE_FLAG_DISABLED;
@@ -1555,9 +1558,12 @@ int register_kprobe(struct kprobe *p) 
		goto out;

	}



	mutex_lock(&text_mutex);	/* Avoiding text modification */

	cpus_read_lock();

	/* Prevent text modification */

	mutex_lock(&text_mutex);

	ret = prepare_kprobe(p);

	mutex_unlock(&text_mutex);

	cpus_read_unlock();

	if (ret)

		goto out;
@@ -1570,7 +1576,6 @@ int register_kprobe(struct kprobe *p) 


	/* Try to optimize kprobe */

	try_to_optimize_kprobe(p);



out:

	mutex_unlock(&kprobe_mutex);