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libfs: take cursors out of list when moving past the end of directory 

that eliminates the last place where we accessed the tail of ->d_subdirs

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2019-09-20 16:32:42 -04:00
parent d4f4de5e5e
commit 26b6c98433
1 changed files with 25 additions and 24 deletions
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49
fs/libfs.c
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@ -92,14 +92,13 @@ EXPORT_SYMBOL(dcache_dir_close);
/*
* 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.
* found, dentry is grabbed and returned to caller.
* If no such element exists, NULL is returned.
*/
static struct list_head *scan_positives(struct dentry *cursor,
static struct dentry *scan_positives(struct dentry *cursor,
struct list_head *p,
loff_t count,
struct dentry **res)
struct dentry *last)
{
struct dentry *dentry = cursor->d_parent, *found = NULL;
@ -127,9 +126,8 @@ static struct list_head *scan_positives(struct dentry *cursor,
}
}
spin_unlock(&dentry->d_lock);
dput(*res);
*res = found;
return p;
dput(last);
return found;
}
loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
@ -149,25 +147,22 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
if (offset != file->f_pos) {
struct dentry *cursor = file->private_data;
struct dentry *to = NULL;
struct list_head *p;
file->f_pos = offset;
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);
if (offset > 2)
to = scan_positives(cursor, &dentry->d_subdirs,
offset - 2, NULL);
spin_lock(&dentry->d_lock);
if (to)
list_move(&cursor->d_child, &to->d_child);
else
list_del_init(&cursor->d_child);
spin_unlock(&dentry->d_lock);
}
spin_unlock(&dentry->d_lock);
dput(to);
file->f_pos = offset;
inode_unlock_shared(dentry->d_inode);
}
return offset;
@ -199,17 +194,23 @@ int dcache_readdir(struct file *file, struct dir_context *ctx)
if (ctx->pos == 2)
p = anchor;
else
else if (!list_empty(&cursor->d_child))
p = &cursor->d_child;
else
return 0;
while ((p = scan_positives(cursor, p, 1, &next)) != anchor) {
while ((next = scan_positives(cursor, p, 1, next)) != NULL) {
if (!dir_emit(ctx, next->d_name.name, next->d_name.len,
d_inode(next)->i_ino, dt_type(d_inode(next))))
break;
ctx->pos++;
p = &next->d_child;
}
spin_lock(&dentry->d_lock);
list_move_tail(&cursor->d_child, p);
if (next)
list_move_tail(&cursor->d_child, &next->d_child);
else
list_del_init(&cursor->d_child);
spin_unlock(&dentry->d_lock);
dput(next);