quota: Refactor dquot_transfer code so that OCFS2 can pass in its references

Currently, __dquot_transfer() acquires its own references of dquot structures
that will be put into inode. But for OCFS2, this creates a lock inversion
between dq_lock (waited on in dqget) and transaction start (started in
ocfs2_setattr). Currently, deadlock is impossible because dq_lock is acquired
only during dquot_acquire and dquot_release and we already hold a reference to
dquot structures in ocfs2_setattr so neither of these functions can be called
while we call dquot_transfer. But this is rather subtle and it is hard to teach
lockdep about it. So provide __dquot_transfer function that can be passed dquot
references directly. OCFS2 can then pass acquired dquot references directly to
__dquot_transfer with proper locking.

Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/quotaops.h b/include/linux/quotaops.h
index 8a7818764a67..370abb1e99cb 100644
--- a/include/linux/quotaops.h
+++ b/include/linux/quotaops.h
@@ -76,6 +76,7 @@ int vfs_get_dqblk(struct super_block *sb, int type, qid_t id,
 int vfs_set_dqblk(struct super_block *sb, int type, qid_t id,
 		struct fs_disk_quota *di);
 
+int __dquot_transfer(struct inode *inode, struct dquot **transfer_to);
 int dquot_transfer(struct inode *inode, struct iattr *iattr);
 int vfs_dq_quota_on_remount(struct super_block *sb);