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authorAl Viro <viro@zeniv.linux.org.uk>2014-08-08 13:08:20 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2014-10-09 02:38:53 -0400
commit9ea459e110df32e60a762f311f7939eaa879601d (patch)
tree3c25c8c4dbe1c21d92ab8e5a52b02c95453490d4 /fs
parentb3ca406f2755c20cea1cc1169672c56dd03c266c (diff)
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delayed mntput
On final mntput() we want fs shutdown to happen before return to userland; however, the only case where we want it happen right there (i.e. where task_work_add won't do) is MNT_INTERNAL victim. Those have to be fully synchronous - failure halfway through module init might count on having vfsmount killed right there. Fortunately, final mntput on MNT_INTERNAL vfsmounts happens on shallow stack. So we handle those synchronously and do an analog of delayed fput logics for everything else. As the result, we are guaranteed that fs shutdown will always happen on shallow stack. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
-rw-r--r--fs/mount.h5
-rw-r--r--fs/namespace.c71
2 files changed, 57 insertions, 19 deletions
diff --git a/fs/mount.h b/fs/mount.h
index 6740a6215529..8f2a14ae38a2 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -29,7 +29,10 @@ struct mount {
struct mount *mnt_parent;
struct dentry *mnt_mountpoint;
struct vfsmount mnt;
- struct rcu_head mnt_rcu;
+ union {
+ struct rcu_head mnt_rcu;
+ struct llist_node mnt_llist;
+ };
#ifdef CONFIG_SMP
struct mnt_pcp __percpu *mnt_pcp;
#else
diff --git a/fs/namespace.c b/fs/namespace.c
index ef42d9bee212..044134315f93 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -23,6 +23,7 @@
#include <linux/proc_ns.h>
#include <linux/magic.h>
#include <linux/bootmem.h>
+#include <linux/task_work.h>
#include "pnode.h"
#include "internal.h"
@@ -957,6 +958,46 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
return ERR_PTR(err);
}
+static void cleanup_mnt(struct mount *mnt)
+{
+ /*
+ * This probably indicates that somebody messed
+ * up a mnt_want/drop_write() pair. If this
+ * happens, the filesystem was probably unable
+ * to make r/w->r/o transitions.
+ */
+ /*
+ * The locking used to deal with mnt_count decrement provides barriers,
+ * so mnt_get_writers() below is safe.
+ */
+ WARN_ON(mnt_get_writers(mnt));
+ if (unlikely(mnt->mnt_pins.first))
+ mnt_pin_kill(mnt);
+ fsnotify_vfsmount_delete(&mnt->mnt);
+ dput(mnt->mnt.mnt_root);
+ deactivate_super(mnt->mnt.mnt_sb);
+ mnt_free_id(mnt);
+ call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
+}
+
+static void __cleanup_mnt(struct rcu_head *head)
+{
+ cleanup_mnt(container_of(head, struct mount, mnt_rcu));
+}
+
+static LLIST_HEAD(delayed_mntput_list);
+static void delayed_mntput(struct work_struct *unused)
+{
+ struct llist_node *node = llist_del_all(&delayed_mntput_list);
+ struct llist_node *next;
+
+ for (; node; node = next) {
+ next = llist_next(node);
+ cleanup_mnt(llist_entry(node, struct mount, mnt_llist));
+ }
+}
+static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
+
static void mntput_no_expire(struct mount *mnt)
{
rcu_read_lock();
@@ -982,24 +1023,18 @@ static void mntput_no_expire(struct mount *mnt)
list_del(&mnt->mnt_instance);
unlock_mount_hash();
- /*
- * This probably indicates that somebody messed
- * up a mnt_want/drop_write() pair. If this
- * happens, the filesystem was probably unable
- * to make r/w->r/o transitions.
- */
- /*
- * The locking used to deal with mnt_count decrement provides barriers,
- * so mnt_get_writers() below is safe.
- */
- WARN_ON(mnt_get_writers(mnt));
- if (unlikely(mnt->mnt_pins.first))
- mnt_pin_kill(mnt);
- fsnotify_vfsmount_delete(&mnt->mnt);
- dput(mnt->mnt.mnt_root);
- deactivate_super(mnt->mnt.mnt_sb);
- mnt_free_id(mnt);
- call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
+ if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
+ struct task_struct *task = current;
+ if (likely(!(task->flags & PF_KTHREAD))) {
+ init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
+ if (!task_work_add(task, &mnt->mnt_rcu, true))
+ return;
+ }
+ if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
+ schedule_delayed_work(&delayed_mntput_work, 1);
+ return;
+ }
+ cleanup_mnt(mnt);
}
void mntput(struct vfsmount *mnt)