diff options
| -rw-r--r-- | fs/libfs.c | 134 |
1 files changed, 69 insertions, 65 deletions
diff --git a/fs/libfs.c b/fs/libfs.c index c9b2850c0f7c..8e023b08a240 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -89,58 +89,47 @@ int dcache_dir_close(struct inode *inode, struct file *file) EXPORT_SYMBOL(dcache_dir_close); /* parent is locked at least shared */ -static struct dentry *next_positive(struct dentry *parent, - struct list_head *from, - int count) +/* + * Returns an element of siblings' list. + * We are looking for <count>th positive after <p>; if + * found, dentry is grabbed and passed to caller via *<res>. + * If no such element exists, the anchor of list is returned + * and *<res> is set to NULL. + */ +static struct list_head *scan_positives(struct dentry *cursor, + struct list_head *p, + loff_t count, + struct dentry **res) { - unsigned *seq = &parent->d_inode->i_dir_seq, n; - struct dentry *res; - struct list_head *p; - bool skipped; - int i; + struct dentry *dentry = cursor->d_parent, *found = NULL; -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) { + spin_lock(&dentry->d_lock); + while ((p = p->next) != &dentry->d_subdirs) { struct dentry *d = list_entry(p, struct dentry, d_child); - if (!simple_positive(d)) { - skipped = true; - } else if (!--i) { - res = d; - break; + // we must at least skip cursors, to avoid livelocks + if (d->d_flags & DCACHE_DENTRY_CURSOR) + continue; + if (simple_positive(d) && !--count) { + spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED); + if (simple_positive(d)) + found = dget_dlock(d); + spin_unlock(&d->d_lock); + if (likely(found)) + break; + count = 1; + } + if (need_resched()) { + list_move(&cursor->d_child, p); + p = &cursor->d_child; + spin_unlock(&dentry->d_lock); + cond_resched(); + spin_lock(&dentry->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); + spin_unlock(&dentry->d_lock); + dput(*res); + *res = found; + return p; } loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence) @@ -158,17 +147,28 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence) return -EINVAL; } if (offset != file->f_pos) { + struct dentry *cursor = file->private_data; + struct dentry *to = NULL; + struct list_head *p; + file->f_pos = offset; - if (file->f_pos >= 2) { - struct dentry *cursor = file->private_data; - struct dentry *to; - loff_t n = file->f_pos - 2; - - inode_lock_shared(dentry->d_inode); - to = next_positive(dentry, &dentry->d_subdirs, n); - move_cursor(cursor, to ? &to->d_child : NULL); - inode_unlock_shared(dentry->d_inode); + inode_lock_shared(dentry->d_inode); + + if (file->f_pos > 2) { + p = scan_positives(cursor, &dentry->d_subdirs, + file->f_pos - 2, &to); + spin_lock(&dentry->d_lock); + list_move(&cursor->d_child, p); + spin_unlock(&dentry->d_lock); + } else { + spin_lock(&dentry->d_lock); + list_del_init(&cursor->d_child); + spin_unlock(&dentry->d_lock); } + + dput(to); + + inode_unlock_shared(dentry->d_inode); } return offset; } @@ -190,25 +190,29 @@ int dcache_readdir(struct file *file, struct dir_context *ctx) { struct dentry *dentry = file->f_path.dentry; struct dentry *cursor = file->private_data; - struct list_head *p = &cursor->d_child; - struct dentry *next; - bool moved = false; + struct list_head *anchor = &dentry->d_subdirs; + struct dentry *next = NULL; + struct list_head *p; if (!dir_emit_dots(file, ctx)) return 0; if (ctx->pos == 2) - p = &dentry->d_subdirs; - while ((next = next_positive(dentry, p, 1)) != NULL) { + p = anchor; + else + p = &cursor->d_child; + + while ((p = scan_positives(cursor, p, 1, &next)) != anchor) { if (!dir_emit(ctx, next->d_name.name, next->d_name.len, d_inode(next)->i_ino, dt_type(d_inode(next)))) break; - moved = true; - p = &next->d_child; ctx->pos++; } - if (moved) - move_cursor(cursor, p); + spin_lock(&dentry->d_lock); + list_move_tail(&cursor->d_child, p); + spin_unlock(&dentry->d_lock); + dput(next); + return 0; } EXPORT_SYMBOL(dcache_readdir); |