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lockless next_positive() 

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2016-06-06 20:55:34 -04:00
parent 4f42c1b5b9
commit ebaaa80e8f
1 changed files with 27 additions and 5 deletions
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32
fs/libfs.c
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@ -89,31 +89,53 @@ static struct dentry *next_positive(struct dentry *parent,
struct list_head *from,
int count)
{
struct dentry *res = NULL;
unsigned *seq = &parent->d_inode->i_dir_seq, n;
struct dentry *res;
struct list_head *p;
bool skipped;
int i;
spin_lock(&parent->d_lock);
retry:
i = count;
skipped = false;
n = smp_load_acquire(seq) & ~1;
res = NULL;
rcu_read_lock();
for (p = from->next; p != &parent->d_subdirs; p = p->next) {
struct dentry *d = list_entry(p, struct dentry, d_child);
if (simple_positive(d) && !--count) {
if (!simple_positive(d)) {
skipped = true;
} else if (!--i) {
res = d;
break;
}
}
spin_unlock(&parent->d_lock);
rcu_read_unlock();
if (skipped) {
smp_rmb();
if (unlikely(*seq != n))
goto retry;
}
return res;
}
static void move_cursor(struct dentry *cursor, struct list_head *after)
{
struct dentry *parent = cursor->d_parent;
unsigned n, *seq = &parent->d_inode->i_dir_seq;
spin_lock(&parent->d_lock);
for (;;) {
n = *seq;
if (!(n & 1) && cmpxchg(seq, n, n + 1) == n)
break;
cpu_relax();
}
__list_del(cursor->d_child.prev, cursor->d_child.next);
if (after)
list_add(&cursor->d_child, after);
else
list_add_tail(&cursor->d_child, &parent->d_subdirs);
smp_store_release(seq, n + 2);
spin_unlock(&parent->d_lock);
}