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Commit 5301a77d authored by Louis Rilling's avatar Louis Rilling Committed by Mark Fasheh
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configfs: Protect configfs_dirent s_links list mutations 



Symlinks to a config_item are listed under its configfs_dirent s_links, but the
list mutations are not protected by any common lock.

This patch uses the configfs_dirent_lock spinlock to add the necessary
protection.

Note: we should also protect the list_empty() test in configfs_detach_prep() but
1/ the lock should not be released immediately because nothing would prevent the
list from being filled after a successful list_empty() test, making the problem
tricky,
2/ this will be solved by the rmdir() vs rename() deadlock bugfix.

Signed-off-by: default avatarLouis Rilling <Louis.Rilling@kerlabs.com>
Signed-off-by: default avatarJoel Becker <joel.becker@oracle.com>
parent 6f610764

fs/configfs/dir.c

+3 −2
Original line number Diff line number Diff line
@@ -37,10 +37,11 @@ 
DECLARE_RWSEM(configfs_rename_sem);

/*

 * Protects mutations of configfs_dirent linkage together with proper i_mutex

 * Also protects mutations of symlinks linkage to target configfs_dirent

 * Mutators of configfs_dirent linkage must *both* have the proper inode locked

 * and configfs_dirent_lock locked, in that order.

 * This allows one to safely traverse configfs_dirent trees without having to

 * lock inodes.

 * This allows one to safely traverse configfs_dirent trees and symlinks without

 * having to lock inodes.

 */

DEFINE_SPINLOCK(configfs_dirent_lock);

fs/configfs/symlink.c

+6 −2
Original line number Diff line number Diff line
@@ -77,12 +77,15 @@ static int create_link(struct config_item *parent_item, 
	sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);

	if (sl) {

		sl->sl_target = config_item_get(item);

		/* FIXME: needs a lock, I'd bet */

		spin_lock(&configfs_dirent_lock);

		list_add(&sl->sl_list, &target_sd->s_links);

		spin_unlock(&configfs_dirent_lock);

		ret = configfs_create_link(sl, parent_item->ci_dentry,

					   dentry);

		if (ret) {

			spin_lock(&configfs_dirent_lock);

			list_del_init(&sl->sl_list);

			spin_unlock(&configfs_dirent_lock);

			config_item_put(item);

			kfree(sl);

		}
@@ -186,8 +189,9 @@ int configfs_unlink(struct inode *dir, struct dentry *dentry) 
		type->ct_item_ops->drop_link(parent_item,

					       sl->sl_target);



	/* FIXME: Needs lock */

	spin_lock(&configfs_dirent_lock);

	list_del_init(&sl->sl_list);

	spin_unlock(&configfs_dirent_lock);



	/* Put reference from create_link() */

	config_item_put(sl->sl_target);