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Message-ID: <20160212095051.GA16878@gmail.com>
Date: Fri, 12 Feb 2016 10:50:51 +0100
From: Ingo Molnar <mingo@...nel.org>
To: akpm@...ux-foundation.org
Cc: torvalds@...ux-foundation.org, aryabinin@...tuozzo.com,
krinkin.m.u@...il.com, mingo@...e.hu, peterz@...radead.org,
linux-kernel@...r.kernel.org,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch 08/10] kernel/locking/lockdep.c: convert hash tables to
hlists
* akpm@...ux-foundation.org <akpm@...ux-foundation.org> wrote:
> From: Andrew Morton <akpm@...ux-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@...il.com>
> Suggested-by: Mike Krinkin <krinkin.m.u@...il.com>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Andrew Morton <akpm@...ux-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@...ux-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@...il.com>
Reported-by: Mike Krinkin <krinkin.m.u@...il.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org
Cc: mm-commits@...r.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.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;
}
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