From: Krzysztof Opasiak <k.opasiak@xxxxxxxxxxx>
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.
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@xxxxxxxxxxx>
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxx>
---
fs/configfs/dir.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/configfs.h | 12 ++++++
2 files changed, 109 insertions(+)
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index c81ce7f..2578ac0 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -1152,6 +1152,103 @@ void configfs_undepend_item(struct configfs_subsystem *subsys,
}
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 *sd, *subsys_sd = NULL;
+ 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) {
+ struct configfs_dirent *p, *root_sd;
+ /*
+ * 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
+ */
+ root_sd = root->cg_item.ci_dentry->d_fsdata;
+ list_for_each_entry(p, &root_sd->s_children, s_sibling) {
+ if (p->s_type & CONFIGFS_DIR &&
+ &target_subsys->su_group.cg_item == p->s_element) {
+ subsys_sd = p;
+ break;
+ }
+ }
+
+ if (!subsys_sd)
+ goto out_root_unlock;
+ } else {
+ subsys_sd = target_subsys->su_group.cg_item.ci_dentry->d_fsdata;
+ }
+
+ spin_lock(&configfs_dirent_lock);
+ ret = configfs_depend_prep(subsys_sd->s_dentry, target);
+ if (ret)
+ goto out_unlock;
+
+ sd = target->ci_dentry->d_fsdata;
+ sd->s_dependent_count += 1;
+
+ ret = 0;
+
+out_unlock:
+ spin_unlock(&configfs_dirent_lock);
+
+ 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);
+
+void configfs_undepend_item_unlocked(struct configfs_subsystem *caller_subsys,
+ struct config_item *target)
+{
+ configfs_undepend_item(NULL, target);
+}
+EXPORT_SYMBOL(configfs_undepend_item_unlocked);
+
static int configfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
int ret = 0;
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index a8a335b..0123610 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -202,4 +202,16 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys);
int configfs_depend_item(struct configfs_subsystem *subsys, struct config_item *target);
void configfs_undepend_item(struct configfs_subsystem *subsys, struct config_item *target);
+/*
+ * These functions can sleep and can alloc with GFP_KERNEL
+ * NOTE: These should be called only underneath configfs callbacks.
+ * NOTE: First parameter is a caller's subsystem, not target's.
+ * WARNING: These cannot be called on newly created item
+ * (in make_group()/make_item() callback)
+ */
+int configfs_depend_item_unlocked(struct configfs_subsystem *caller_subsys,
+ struct config_item *target);
+void configfs_undepend_item_unlocked(struct configfs_subsystem *caller_subsys,
+ struct config_item *target);
+
#endif /* _CONFIGFS_H_ */
--
1.9.1
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