Added an i_state flag I_INUSE and helpers to set/clear/test the bit.
The 'inuse' lock is an 'advisory' inode lock, which also provides
may_delete() protection, so can be used to extend exclusive create
protection beyond parent->i_mutex lock among cooperating users.
This is going to be used by overlayfs to get exclusive ownership
on upper and work dirs among overlayfs mounts.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/btrfs/ioctl.c | 3 +++
fs/inode.c | 40 ++++++++++++++++++++++++++++++++++++++++
fs/namei.c | 3 +++
include/linux/fs.h | 16 ++++++++++++++++
4 files changed, 62 insertions(+)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index e176375..17fa239 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -782,6 +782,7 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
* 9. We can't remove a root or mountpoint.
* 10. We don't allow removal of NFS sillyrenamed files; it's handled by
* nfs_async_unlink().
+ * 11. We don't allow removal of inodes marked 'inuse'.
*/
static int btrfs_may_delete(struct inode *dir, struct dentry *victim, int isdir)
@@ -813,6 +814,8 @@ static int btrfs_may_delete(struct inode *dir, struct dentry *victim, int isdir)
return -ENOENT;
if (victim->d_flags & DCACHE_NFSFS_RENAMED)
return -EBUSY;
+ if (inode_inuse(d_inode(victim)))
+ return -EBUSY;
return 0;
}
diff --git a/fs/inode.c b/fs/inode.c
index db59147..0552c8b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2120,3 +2120,43 @@ struct timespec current_time(struct inode *inode)
return timespec_trunc(now, inode->i_sb->s_time_gran);
}
EXPORT_SYMBOL(current_time);
+
+/**
+ * inode_inuse_trylock - try to get an exclusive 'inuse' lock on inode
+ * @inode: inode being locked
+ *
+ * The 'inuse' lock is an 'advisory' inode lock, which also provides
+ * may_delete() protection, so can be used to extend exclusive create
+ * protection beyond parent->i_mutex lock among cooperating users.
+ * Used by overlayfs to get exclusive ownership on upper and work dirs
+ * among overlayfs mounts.
+ *
+ * Return true if I_INUSE flag was set by this call.
+ */
+bool inode_inuse_trylock(struct inode *inode)
+{
+ bool locked = false;
+
+ spin_lock(&inode->i_lock);
+ if (!(inode->i_state & (I_FREEING|I_WILL_FREE|I_INUSE))) {
+ inode->i_state |= I_INUSE;
+ locked = true;
+ }
+ spin_unlock(&inode->i_lock);
+ return locked;
+}
+EXPORT_SYMBOL(inode_inuse_trylock);
+
+/*
+ * Non-cooperating users should not be calling this functions and cooperating
+ * users should call this function only if they have the exclusive 'inuse' lock.
+ */
+void inode_inuse_unlock(struct inode *inode)
+{
+ WARN_ON(!inode_inuse(inode));
+
+ spin_lock(&inode->i_lock);
+ inode->i_state &= ~I_INUSE;
+ spin_unlock(&inode->i_lock);
+}
+EXPORT_SYMBOL(inode_inuse_unlock);
diff --git a/fs/namei.c b/fs/namei.c
index 837da8b..c371b25 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2790,6 +2790,7 @@ EXPORT_SYMBOL(__check_sticky);
* 10. We can't remove a root or mountpoint.
* 11. We don't allow removal of NFS sillyrenamed files; it's handled by
* nfs_async_unlink().
+ * 12. We don't allow removal of inodes marked 'inuse'.
*/
static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
{
@@ -2823,6 +2824,8 @@ static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
return -ENOENT;
if (victim->d_flags & DCACHE_NFSFS_RENAMED)
return -EBUSY;
+ if (inode_inuse(d_inode(victim)))
+ return -EBUSY;
return 0;
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index aab10f9..1420e8b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1864,6 +1864,7 @@ struct super_operations {
#define IS_AUTOMOUNT(inode) ((inode)->i_flags & S_AUTOMOUNT)
#define IS_NOSEC(inode) ((inode)->i_flags & S_NOSEC)
#define IS_DAX(inode) ((inode)->i_flags & S_DAX)
+#define IS_INUSE(inode) ((inode)->i_flags & S_INUSE)
#define IS_WHITEOUT(inode) (S_ISCHR(inode->i_mode) && \
(inode)->i_rdev == WHITEOUT_DEV)
@@ -1929,6 +1930,13 @@ static inline bool HAS_UNMAPPED_ID(struct inode *inode)
* wb stat updates to grab mapping->tree_lock. See
* inode_switch_wb_work_fn() for details.
*
+ * I_INUSE An 'advisory' bit to get exclusive ownership on inode
+ * using inode_inuse_trylock(). Also provides may_delete()
+ * protection, so can be used to extend exclusive create
+ * protection beyond parent->i_mutex lock.
+ * Used by overlayfs to get exclusive ownership on upper
+ * and work dirs among overlayfs mounts.
+ *
* Q: What is the difference between I_WILL_FREE and I_FREEING?
*/
#define I_DIRTY_SYNC (1 << 0)
@@ -1949,6 +1957,7 @@ static inline bool HAS_UNMAPPED_ID(struct inode *inode)
#define __I_DIRTY_TIME_EXPIRED 12
#define I_DIRTY_TIME_EXPIRED (1 << __I_DIRTY_TIME_EXPIRED)
#define I_WB_SWITCH (1 << 13)
+#define I_INUSE (1 << 14)
#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)
#define I_DIRTY_ALL (I_DIRTY | I_DIRTY_TIME)
@@ -3258,5 +3267,12 @@ static inline bool dir_relax_shared(struct inode *inode)
extern bool path_noexec(const struct path *path);
extern void inode_nohighmem(struct inode *inode);
+extern bool inode_inuse_trylock(struct inode *inode);
+extern void inode_inuse_unlock(struct inode *inode);
+
+static inline bool inode_inuse(struct inode *inode)
+{
+ return inode->i_state & I_INUSE;
+}
#endif /* _LINUX_FS_H */
--
2.7.4
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