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Commit f2545b2d authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

jump_label: Reorder hotplug lock and jump_label_lock 



The conversion of the hotplug locking to a percpu rwsem unearthed lock
ordering issues all over the place.

The jump_label code has two issues:

 1) Nested get_online_cpus() invocations

 2) Ordering problems vs. the cpus rwsem and the jump_label_mutex

To cure these, the following lock order has been established;

   cpus_rwsem -> jump_label_lock -> text_mutex

Even if not all architectures need protection against CPU hotplug, taking
cpus_rwsem before jump_label_lock is now mandatory in code pathes which
actually modify code and therefor need text_mutex protection.

Move the get_online_cpus() invocations into the core jump label code and
establish the proper lock order where required.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatar"David S. Miller" <davem@davemloft.net>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Link: http://lkml.kernel.org/r/20170524081549.025830817@linutronix.de
parent a63fbed7

arch/mips/kernel/jump_label.c

+0 −2
Original line number Diff line number Diff line
@@ -58,7 +58,6 @@ void arch_jump_label_transform(struct jump_entry *e, 
		insn.word = 0; /* nop */

	}



	get_online_cpus();

	mutex_lock(&text_mutex);

	if (IS_ENABLED(CONFIG_CPU_MICROMIPS)) {

		insn_p->halfword[0] = insn.word >> 16;
@@ -70,7 +69,6 @@ void arch_jump_label_transform(struct jump_entry *e, 
			   (unsigned long)insn_p + sizeof(*insn_p));



	mutex_unlock(&text_mutex);

	put_online_cpus();

}



#endif /* HAVE_JUMP_LABEL */

arch/sparc/kernel/jump_label.c

+0 −2
Original line number Diff line number Diff line
@@ -41,12 +41,10 @@ void arch_jump_label_transform(struct jump_entry *entry, 
		val = 0x01000000;

	}



	get_online_cpus();

	mutex_lock(&text_mutex);

	*insn = val;

	flushi(insn);

	mutex_unlock(&text_mutex);

	put_online_cpus();

}



#endif

arch/tile/kernel/jump_label.c

+0 −2
Original line number Diff line number Diff line
@@ -45,14 +45,12 @@ static void __jump_label_transform(struct jump_entry *e, 
void arch_jump_label_transform(struct jump_entry *e,

				enum jump_label_type type)

{

	get_online_cpus();

	mutex_lock(&text_mutex);



	__jump_label_transform(e, type);

	flush_icache_range(e->code, e->code + sizeof(tilegx_bundle_bits));



	mutex_unlock(&text_mutex);

	put_online_cpus();

}



__init_or_module void arch_jump_label_transform_static(struct jump_entry *e,

arch/x86/kernel/jump_label.c

+0 −2
Original line number Diff line number Diff line
@@ -105,11 +105,9 @@ static void __jump_label_transform(struct jump_entry *entry, 
void arch_jump_label_transform(struct jump_entry *entry,

			       enum jump_label_type type)

{

	get_online_cpus();

	mutex_lock(&text_mutex);

	__jump_label_transform(entry, type, NULL, 0);

	mutex_unlock(&text_mutex);

	put_online_cpus();

}



static enum {

kernel/jump_label.c

+14 −6
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/static_key.h>

#include <linux/jump_label_ratelimit.h>

#include <linux/bug.h>

#include <linux/cpu.h>



#ifdef HAVE_JUMP_LABEL
@@ -124,6 +125,7 @@ void static_key_slow_inc(struct static_key *key) 
			return;

	}



	cpus_read_lock();

	jump_label_lock();

	if (atomic_read(&key->enabled) == 0) {

		atomic_set(&key->enabled, -1);
@@ -133,12 +135,14 @@ void static_key_slow_inc(struct static_key *key) 
		atomic_inc(&key->enabled);

	}

	jump_label_unlock();

	cpus_read_unlock();

}

EXPORT_SYMBOL_GPL(static_key_slow_inc);



static void __static_key_slow_dec(struct static_key *key,

		unsigned long rate_limit, struct delayed_work *work)

{

	cpus_read_lock();

	/*

	 * The negative count check is valid even when a negative

	 * key->enabled is in use by static_key_slow_inc(); a
@@ -149,6 +153,7 @@ static void __static_key_slow_dec(struct static_key *key, 
	if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {

		WARN(atomic_read(&key->enabled) < 0,

		     "jump label: negative count!\n");

		cpus_read_unlock();

		return;

	}
@@ -159,6 +164,7 @@ static void __static_key_slow_dec(struct static_key *key, 
		jump_label_update(key);

	}

	jump_label_unlock();

	cpus_read_unlock();

}



static void jump_label_update_timeout(struct work_struct *work)
@@ -334,6 +340,7 @@ void __init jump_label_init(void) 
	if (static_key_initialized)

		return;



	cpus_read_lock();

	jump_label_lock();

	jump_label_sort_entries(iter_start, iter_stop);
@@ -353,6 +360,7 @@ void __init jump_label_init(void) 
	}

	static_key_initialized = true;

	jump_label_unlock();

	cpus_read_unlock();

}



#ifdef CONFIG_MODULES
@@ -590,28 +598,28 @@ jump_label_module_notify(struct notifier_block *self, unsigned long val, 
	struct module *mod = data;

	int ret = 0;



	cpus_read_lock();

	jump_label_lock();



	switch (val) {

	case MODULE_STATE_COMING:

		jump_label_lock();

		ret = jump_label_add_module(mod);

		if (ret) {

			WARN(1, "Failed to allocatote memory: jump_label may not work properly.\n");

			jump_label_del_module(mod);

		}

		jump_label_unlock();

		break;

	case MODULE_STATE_GOING:

		jump_label_lock();

		jump_label_del_module(mod);

		jump_label_unlock();

		break;

	case MODULE_STATE_LIVE:

		jump_label_lock();

		jump_label_invalidate_module_init(mod);

		jump_label_unlock();

		break;

	}



	jump_label_unlock();

	cpus_read_unlock();



	return notifier_from_errno(ret);

}