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authorKrzysztof Opasiak <k.opasiak@samsung.com>2015-12-11 16:06:12 +0100
committerNicholas Bellinger <nab@linux-iscsi.org>2015-12-20 18:04:03 -0800
commitd79d75b5c5182fd94225996db71e06f9cbc7faed (patch)
tree8e0b9def43d58ee4d8775896e683a8128fa7048f /fs/configfs
parent9a70adfff3379a6511483bd60dac06fda49b14a8 (diff)
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fs: configfs: Add unlocked version of configfs_depend_item()
This change is necessary for the SCSI target usb gadget composed with configfs. In this case configfs will be used for two different purposes: to compose a usb gadget and to configure the target part. If an instance of tcm function is created in $CONFIGFS_ROOT/usb_gadget/<gadget>/functions a tpg can be created in $CONFIGFS_ROOT/target/usb_gadget/<wwn>/, but after a tpg is created the tcm function must not be removed until its corresponding tpg is gone. While the configfs_depend/undepend_item() are meant exactly for creating this kind of dependencies, they are not suitable if the other kernel subsystem happens to be another subsystem in configfs, so this patch adds unlocked versions meant for configfs callbacks. Above description has been provided by: Andrzej Pietrasiewicz <andrzej.p@samsung.com> In configfs_depend_item() we have to consider two possible cases: 1) When we are called to depend another item in the same subsystem as caller In this case we should skip locking configfs root as we know that configfs is in valid state and our subsystem will not be unregistered during this call. 2) When we are called to depend item in different subsystem than our caller In this case we are also sure that configfs is in valid state but we have to lock root of configfs to avoid unregistration of target's subsystem. As it is other than caller's subsystem, there may be nothing what protects us against unregistration of that subsystem. Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com> Cc: Joel Becker <jlbec@evilplan.org> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Diffstat (limited to 'fs/configfs')
-rw-r--r--fs/configfs/dir.c73
1 files changed, 73 insertions, 0 deletions
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 3873ac10b68c..8fd032ad6920 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -1171,6 +1171,79 @@ void configfs_undepend_item(struct config_item *target)
}
EXPORT_SYMBOL(configfs_undepend_item);
+/*
+ * caller_subsys is a caller's subsystem not target's. This is used to
+ * determine if we should lock root and check subsys or not. When we are
+ * in the same subsystem as our target there is no need to do locking as
+ * we know that subsys is valid and is not unregistered during this function
+ * as we are called from callback of one of his children and VFS holds a lock
+ * on some inode. Otherwise we have to lock our root to ensure that target's
+ * subsystem it is not unregistered during this function.
+ */
+int configfs_depend_item_unlocked(struct configfs_subsystem *caller_subsys,
+ struct config_item *target)
+{
+ struct configfs_subsystem *target_subsys;
+ struct config_group *root, *parent;
+ struct configfs_dirent *subsys_sd;
+ int ret = -ENOENT;
+
+ /* Disallow this function for configfs root */
+ if (configfs_is_root(target))
+ return -EINVAL;
+
+ parent = target->ci_group;
+ /*
+ * This may happen when someone is trying to depend root
+ * directory of some subsystem
+ */
+ if (configfs_is_root(&parent->cg_item)) {
+ target_subsys = to_configfs_subsystem(to_config_group(target));
+ root = parent;
+ } else {
+ target_subsys = parent->cg_subsys;
+ /* Find a cofnigfs root as we may need it for locking */
+ for (root = parent; !configfs_is_root(&root->cg_item);
+ root = root->cg_item.ci_group)
+ ;
+ }
+
+ if (target_subsys != caller_subsys) {
+ /*
+ * We are in other configfs subsystem, so we have to do
+ * additional locking to prevent other subsystem from being
+ * unregistered
+ */
+ mutex_lock(&d_inode(root->cg_item.ci_dentry)->i_mutex);
+
+ /*
+ * As we are trying to depend item from other subsystem
+ * we have to check if this subsystem is still registered
+ */
+ subsys_sd = configfs_find_subsys_dentry(
+ root->cg_item.ci_dentry->d_fsdata,
+ &target_subsys->su_group.cg_item);
+ if (!subsys_sd)
+ goto out_root_unlock;
+ } else {
+ subsys_sd = target_subsys->su_group.cg_item.ci_dentry->d_fsdata;
+ }
+
+ /* Now we can execute core of depend item */
+ ret = configfs_do_depend_item(subsys_sd->s_dentry, target);
+
+ if (target_subsys != caller_subsys)
+out_root_unlock:
+ /*
+ * We were called from subsystem other than our target so we
+ * took some locks so now it's time to release them
+ */
+ mutex_unlock(&d_inode(root->cg_item.ci_dentry)->i_mutex);
+
+ return ret;
+}
+EXPORT_SYMBOL(configfs_depend_item_unlocked);
+
static int configfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
int ret = 0;