Re: [patch 08/10] kernel/locking/lockdep.c: convert hash tables to hlists

[Ingo Molnar <mingo@kernel.org>]

* akpm@linux-foundation.org <akpm@linux-foundation.org> wrote:

> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: kernel/locking/lockdep.c: convert hash tables to hlists
> 
> Mike said:
> 
> : CONFIG_UBSAN_ALIGNMENT breaks x86-64 kernel with lockdep enabled, i.  e
> : kernel with CONFIG_UBSAN_ALIGNMENT fails to load without even any error
> : message.
> : 
> : The problem is that ubsan callbacks use spinlocks and might be called
> : before lockdep is initialized.  Particularly this line in the
> : reserve_ebda_region function causes problem:
> : 
> : lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
> : 
> : If i put lockdep_init() before reserve_ebda_region call in
> : x86_64_start_reservations kernel loads well.
> 
> Fix this ordering issue permanently: change lockdep so that it uses hlists
> for the hash tables.  Unlike a list_head, an hlist_head is in its
> initialized state when it is all-zeroes, so lockdep is ready for operation
> immediately upon boot - lockdep_init() need not have run.
> 
> The patch will also save some memory.
> 
> lockdep_init() and lockdep_initialized can be done away with now - a 4.6
> patch has been prepared to do this.
> 
> Reported-by: Mike Krinkin <krinkin.m.u@gmail.com>
> Suggested-by: Mike Krinkin <krinkin.m.u@gmail.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  include/linux/lockdep.h  |    4 +--
>  kernel/locking/lockdep.c |   42 ++++++++++++++++---------------------
>  2 files changed, 21 insertions(+), 25 deletions(-)

Hm, so I already have the patch below queued up for v4.6, in the locking tree, 
plus the followup lockdep_init() patch as well.

Didn't want to merge this relatively intrusive patch late in the -rc cycle, as it 
appears this is not a regression: CONFIG_UBSAN_ALIGNMENT apparently never worked 
on x86_64.

But no big feelings either way.

Thanks,

	Ingo

===================================>
>From a63f38cc4ccfa076f87fc3d0c276ee62e710f953 Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@linux-foundation.org>
Date: Wed, 3 Feb 2016 13:44:12 -0800
Subject: [PATCH] locking/lockdep: Convert hash tables to hlists

Mike said:

: CONFIG_UBSAN_ALIGNMENT breaks x86-64 kernel with lockdep enabled, i.e.
: kernel with CONFIG_UBSAN_ALIGNMENT=y fails to load without even any error
: message.
:
: The problem is that ubsan callbacks use spinlocks and might be called
: before lockdep is initialized.  Particularly this line in the
: reserve_ebda_region function causes problem:
:
: lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
:
: If i put lockdep_init() before reserve_ebda_region call in
: x86_64_start_reservations kernel loads well.

Fix this ordering issue permanently: change lockdep so that it uses hlists
for the hash tables.  Unlike a list_head, an hlist_head is in its
initialized state when it is all-zeroes, so lockdep is ready for operation
immediately upon boot - lockdep_init() need not have run.

The patch will also save some memory.

Probably lockdep_init() and lockdep_initialized can be done away with now.

Suggested-by: Mike Krinkin <krinkin.m.u@gmail.com>
Reported-by: Mike Krinkin <krinkin.m.u@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: mm-commits@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/lockdep.h  |  4 ++--
 kernel/locking/lockdep.c | 42 +++++++++++++++++++-----------------------
 2 files changed, 21 insertions(+), 25 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index c57e424d914b..4dca42fd32f5 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -66,7 +66,7 @@ struct lock_class {
 	/*
 	 * class-hash:
 	 */
-	struct list_head		hash_entry;
+	struct hlist_node		hash_entry;
 
 	/*
 	 * global list of all lock-classes:
@@ -199,7 +199,7 @@ struct lock_chain {
 	u8				irq_context;
 	u8				depth;
 	u16				base;
-	struct list_head		entry;
+	struct hlist_node		entry;
 	u64				chain_key;
 };
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c7710e4092ef..716547fdb873 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -292,7 +292,7 @@ LIST_HEAD(all_lock_classes);
 #define __classhashfn(key)	hash_long((unsigned long)key, CLASSHASH_BITS)
 #define classhashentry(key)	(classhash_table + __classhashfn((key)))
 
-static struct list_head classhash_table[CLASSHASH_SIZE];
+static struct hlist_head classhash_table[CLASSHASH_SIZE];
 
 /*
  * We put the lock dependency chains into a hash-table as well, to cache
@@ -303,7 +303,7 @@ static struct list_head classhash_table[CLASSHASH_SIZE];
 #define __chainhashfn(chain)	hash_long(chain, CHAINHASH_BITS)
 #define chainhashentry(chain)	(chainhash_table + __chainhashfn((chain)))
 
-static struct list_head chainhash_table[CHAINHASH_SIZE];
+static struct hlist_head chainhash_table[CHAINHASH_SIZE];
 
 /*
  * The hash key of the lock dependency chains is a hash itself too:
@@ -666,7 +666,7 @@ static inline struct lock_class *
 look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
 {
 	struct lockdep_subclass_key *key;
-	struct list_head *hash_head;
+	struct hlist_head *hash_head;
 	struct lock_class *class;
 
 #ifdef CONFIG_DEBUG_LOCKDEP
@@ -719,7 +719,7 @@ look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
 		return NULL;
 
-	list_for_each_entry_rcu(class, hash_head, hash_entry) {
+	hlist_for_each_entry_rcu(class, hash_head, hash_entry) {
 		if (class->key == key) {
 			/*
 			 * Huh! same key, different name? Did someone trample
@@ -742,7 +742,7 @@ static inline struct lock_class *
 register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
 {
 	struct lockdep_subclass_key *key;
-	struct list_head *hash_head;
+	struct hlist_head *hash_head;
 	struct lock_class *class;
 
 	DEBUG_LOCKS_WARN_ON(!irqs_disabled());
@@ -774,7 +774,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
 	 * We have to do the hash-walk again, to avoid races
 	 * with another CPU:
 	 */
-	list_for_each_entry_rcu(class, hash_head, hash_entry) {
+	hlist_for_each_entry_rcu(class, hash_head, hash_entry) {
 		if (class->key == key)
 			goto out_unlock_set;
 	}
@@ -805,7 +805,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
 	 * We use RCU's safe list-add method to make
 	 * parallel walking of the hash-list safe:
 	 */
-	list_add_tail_rcu(&class->hash_entry, hash_head);
+	hlist_add_head_rcu(&class->hash_entry, hash_head);
 	/*
 	 * Add it to the global list of classes:
 	 */
@@ -2021,7 +2021,7 @@ static inline int lookup_chain_cache(struct task_struct *curr,
 				     u64 chain_key)
 {
 	struct lock_class *class = hlock_class(hlock);
-	struct list_head *hash_head = chainhashentry(chain_key);
+	struct hlist_head *hash_head = chainhashentry(chain_key);
 	struct lock_chain *chain;
 	struct held_lock *hlock_curr;
 	int i, j;
@@ -2037,7 +2037,7 @@ static inline int lookup_chain_cache(struct task_struct *curr,
 	 * We can walk it lock-free, because entries only get added
 	 * to the hash:
 	 */
-	list_for_each_entry_rcu(chain, hash_head, entry) {
+	hlist_for_each_entry_rcu(chain, hash_head, entry) {
 		if (chain->chain_key == chain_key) {
 cache_hit:
 			debug_atomic_inc(chain_lookup_hits);
@@ -2061,7 +2061,7 @@ static inline int lookup_chain_cache(struct task_struct *curr,
 	/*
 	 * We have to walk the chain again locked - to avoid duplicates:
 	 */
-	list_for_each_entry(chain, hash_head, entry) {
+	hlist_for_each_entry(chain, hash_head, entry) {
 		if (chain->chain_key == chain_key) {
 			graph_unlock();
 			goto cache_hit;
@@ -2095,7 +2095,7 @@ static inline int lookup_chain_cache(struct task_struct *curr,
 		}
 		chain_hlocks[chain->base + j] = class - lock_classes;
 	}
-	list_add_tail_rcu(&chain->entry, hash_head);
+	hlist_add_head_rcu(&chain->entry, hash_head);
 	debug_atomic_inc(chain_lookup_misses);
 	inc_chains();
 
@@ -3879,7 +3879,7 @@ void lockdep_reset(void)
 	nr_process_chains = 0;
 	debug_locks = 1;
 	for (i = 0; i < CHAINHASH_SIZE; i++)
-		INIT_LIST_HEAD(chainhash_table + i);
+		INIT_HLIST_HEAD(chainhash_table + i);
 	raw_local_irq_restore(flags);
 }
 
@@ -3898,7 +3898,7 @@ static void zap_class(struct lock_class *class)
 	/*
 	 * Unhash the class and remove it from the all_lock_classes list:
 	 */
-	list_del_rcu(&class->hash_entry);
+	hlist_del_rcu(&class->hash_entry);
 	list_del_rcu(&class->lock_entry);
 
 	RCU_INIT_POINTER(class->key, NULL);
@@ -3921,7 +3921,7 @@ static inline int within(const void *addr, void *start, unsigned long size)
 void lockdep_free_key_range(void *start, unsigned long size)
 {
 	struct lock_class *class;
-	struct list_head *head;
+	struct hlist_head *head;
 	unsigned long flags;
 	int i;
 	int locked;
@@ -3934,9 +3934,7 @@ void lockdep_free_key_range(void *start, unsigned long size)
 	 */
 	for (i = 0; i < CLASSHASH_SIZE; i++) {
 		head = classhash_table + i;
-		if (list_empty(head))
-			continue;
-		list_for_each_entry_rcu(class, head, hash_entry) {
+		hlist_for_each_entry_rcu(class, head, hash_entry) {
 			if (within(class->key, start, size))
 				zap_class(class);
 			else if (within(class->name, start, size))
@@ -3966,7 +3964,7 @@ void lockdep_free_key_range(void *start, unsigned long size)
 void lockdep_reset_lock(struct lockdep_map *lock)
 {
 	struct lock_class *class;
-	struct list_head *head;
+	struct hlist_head *head;
 	unsigned long flags;
 	int i, j;
 	int locked;
@@ -3991,9 +3989,7 @@ void lockdep_reset_lock(struct lockdep_map *lock)
 	locked = graph_lock();
 	for (i = 0; i < CLASSHASH_SIZE; i++) {
 		head = classhash_table + i;
-		if (list_empty(head))
-			continue;
-		list_for_each_entry_rcu(class, head, hash_entry) {
+		hlist_for_each_entry_rcu(class, head, hash_entry) {
 			int match = 0;
 
 			for (j = 0; j < NR_LOCKDEP_CACHING_CLASSES; j++)
@@ -4031,10 +4027,10 @@ void lockdep_init(void)
 		return;
 
 	for (i = 0; i < CLASSHASH_SIZE; i++)
-		INIT_LIST_HEAD(classhash_table + i);
+		INIT_HLIST_HEAD(classhash_table + i);
 
 	for (i = 0; i < CHAINHASH_SIZE; i++)
-		INIT_LIST_HEAD(chainhash_table + i);
+		INIT_HLIST_HEAD(chainhash_table + i);
 
 	lockdep_initialized = 1;
 }