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Subject[PATCH 2/6] vfs: Change inode_hash_lock to a seqlock [ver #2]
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Date
Change inode_hash_lock to a seqlock so that a subsequent patch can try
doing lockless searches of the icache, but we can still force a retry under
lock by bumping the sequence counter.

For the moment, all locking is done with read_seqlock_excl(), which is just
a wrapper around spin_lock() and doesn't bump the sequence counter at all.

Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/inode.c | 62 ++++++++++++++++++++++++++++++------------------------------
1 file changed, 31 insertions(+), 31 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 00bb48ca3642..cc2b08d82618 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -56,7 +56,7 @@
static unsigned int i_hash_mask __read_mostly;
static unsigned int i_hash_shift __read_mostly;
static struct hlist_head *inode_hashtable __read_mostly;
-static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock);
+static __cacheline_aligned_in_smp DEFINE_SEQLOCK(inode_hash_lock);

/*
* Empty aops. Can be used for the cases where the user does not
@@ -477,11 +477,11 @@ void __insert_inode_hash(struct inode *inode, unsigned long hashval)
{
struct hlist_head *b = inode_hashtable + hash(inode->i_sb, hashval);

- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
spin_lock(&inode->i_lock);
hlist_add_head(&inode->i_hash, b);
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
}
EXPORT_SYMBOL(__insert_inode_hash);

@@ -493,11 +493,11 @@ EXPORT_SYMBOL(__insert_inode_hash);
*/
void __remove_inode_hash(struct inode *inode)
{
- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
spin_lock(&inode->i_lock);
hlist_del_init(&inode->i_hash);
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
}
EXPORT_SYMBOL(__remove_inode_hash);

@@ -514,13 +514,13 @@ void rehash_inode(struct inode *inode, unsigned long hashval,
{
struct hlist_head *b = inode_hashtable + hash(inode->i_sb, hashval);

- spin_lock(&inode_hash_lock);
+ write_seqlock(&inode_hash_lock);
spin_lock(&inode->i_lock);
hlist_del_init(&inode->i_hash);
reset(inode, hashval, data);
hlist_add_head(&inode->i_hash, b);
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_hash_lock);
+ write_sequnlock(&inode_hash_lock);
}
EXPORT_SYMBOL(rehash_inode);

@@ -1076,14 +1076,14 @@ struct inode *inode_insert5(struct inode *inode, unsigned long hashval,
bool creating = inode->i_state & I_CREATING;

again:
- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
old = find_inode(inode->i_sb, head, test, data);
if (unlikely(old)) {
/*
* Uhhuh, somebody else created the same inode under us.
* Use the old inode instead of the preallocated one.
*/
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
if (IS_ERR(old))
return NULL;
wait_on_inode(old);
@@ -1110,7 +1110,7 @@ struct inode *inode_insert5(struct inode *inode, unsigned long hashval,
if (!creating)
inode_sb_list_add(inode);
unlock:
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);

return inode;
}
@@ -1174,9 +1174,9 @@ struct inode *iget_locked(struct super_block *sb, unsigned long ino)
struct hlist_head *head = inode_hashtable + hash(sb, ino);
struct inode *inode;
again:
- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
inode = find_inode_fast(sb, head, ino);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
if (inode) {
if (IS_ERR(inode))
return NULL;
@@ -1192,17 +1192,17 @@ struct inode *iget_locked(struct super_block *sb, unsigned long ino)
if (inode) {
struct inode *old;

- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
/* We released the lock, so.. */
old = find_inode_fast(sb, head, ino);
if (!old) {
inode->i_ino = ino;
spin_lock(&inode->i_lock);
inode->i_state = I_NEW;
- hlist_add_head(&inode->i_hash, head);
+ hlist_add_head_rcu(&inode->i_hash, head);
spin_unlock(&inode->i_lock);
inode_sb_list_add(inode);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);

/* Return the locked inode with I_NEW set, the
* caller is responsible for filling in the contents
@@ -1215,7 +1215,7 @@ struct inode *iget_locked(struct super_block *sb, unsigned long ino)
* us. Use the old inode instead of the one we just
* allocated.
*/
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
destroy_inode(inode);
if (IS_ERR(old))
return NULL;
@@ -1242,14 +1242,14 @@ static int test_inode_iunique(struct super_block *sb, unsigned long ino)
struct hlist_head *b = inode_hashtable + hash(sb, ino);
struct inode *inode;

- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
hlist_for_each_entry(inode, b, i_hash) {
if (inode->i_ino == ino && inode->i_sb == sb) {
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
return 0;
}
}
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);

return 1;
}
@@ -1332,9 +1332,9 @@ struct inode *ilookup5_nowait(struct super_block *sb, unsigned long hashval,
struct hlist_head *head = inode_hashtable + hash(sb, hashval);
struct inode *inode;

- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
inode = find_inode(sb, head, test, data);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);

return IS_ERR(inode) ? NULL : inode;
}
@@ -1387,9 +1387,9 @@ struct inode *ilookup(struct super_block *sb, unsigned long ino)
struct hlist_head *head = inode_hashtable + hash(sb, ino);
struct inode *inode;
again:
- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
inode = find_inode_fast(sb, head, ino);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);

if (inode) {
if (IS_ERR(inode))
@@ -1437,7 +1437,7 @@ struct inode *find_inode_nowait(struct super_block *sb,
struct inode *inode, *ret_inode = NULL;
int mval;

- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
hlist_for_each_entry(inode, head, i_hash) {
if (inode->i_sb != sb)
continue;
@@ -1449,7 +1449,7 @@ struct inode *find_inode_nowait(struct super_block *sb,
goto out;
}
out:
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
return ret_inode;
}
EXPORT_SYMBOL(find_inode_nowait);
@@ -1462,7 +1462,7 @@ int insert_inode_locked(struct inode *inode)

while (1) {
struct inode *old = NULL;
- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
hlist_for_each_entry(old, head, i_hash) {
if (old->i_ino != ino)
continue;
@@ -1480,17 +1480,17 @@ int insert_inode_locked(struct inode *inode)
inode->i_state |= I_NEW | I_CREATING;
hlist_add_head(&inode->i_hash, head);
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
return 0;
}
if (unlikely(old->i_state & I_CREATING)) {
spin_unlock(&old->i_lock);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
return -EBUSY;
}
__iget(old);
spin_unlock(&old->i_lock);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
wait_on_inode(old);
if (unlikely(!inode_unhashed(old))) {
iput(old);
@@ -1932,10 +1932,10 @@ static void __wait_on_freeing_inode(struct inode *inode)
wq = bit_waitqueue(&inode->i_state, __I_NEW);
prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_hash_lock);
+ read_sequnlock_excl(&inode_hash_lock);
schedule();
finish_wait(wq, &wait.wq_entry);
- spin_lock(&inode_hash_lock);
+ read_seqlock_excl(&inode_hash_lock);
}

static __initdata unsigned long ihash_entries;
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