Coda: add spin lock to protect accesses to struct coda_inode_info.

We mostly need it to protect cached user permissions. The c_flags field
is advisory, reading the wrong value is harmless and in the worst case
we hit a slow path where we have to make an extra upcall to the
userspace cache manager when revalidating a dentry or inode.

Signed-off-by: Yoshihisa Abe <yoshiabe@cs.cmu.edu>
Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 5 deletions

diff --git a/fs/coda/cnode.c b/fs/coda/cnode.c
index a7a7809..6022405 100644
--- a/fs/coda/cnode.c
+++ b/fs/coda/cnode.c
@@ -45,13 +45,15 @@ static void coda_fill_inode(struct inode *inode, struct coda_vattr *attr)
 static int coda_test_inode(struct inode *inode, void *data)
 {
 	struct CodaFid *fid = (struct CodaFid *)data;
-	return coda_fideq(&(ITOC(inode)->c_fid), fid);
+	struct coda_inode_info *cii = ITOC(inode);
+	return coda_fideq(&cii->c_fid, fid);
 }
 
 static int coda_set_inode(struct inode *inode, void *data)
 {
 	struct CodaFid *fid = (struct CodaFid *)data;
-	ITOC(inode)->c_fid = *fid;
+	struct coda_inode_info *cii = ITOC(inode);
+	cii->c_fid = *fid;
 	return 0;
 }
 
@@ -71,6 +73,7 @@ struct inode * coda_iget(struct super_block * sb, struct CodaFid * fid,
 		cii = ITOC(inode);
 		/* we still need to set i_ino for things like stat(2) */
 		inode->i_ino = hash;
+		/* inode is locked and unique, no need to grab cii->c_lock */
 		cii->c_mapcount = 0;
 		unlock_new_inode(inode);
 	}
@@ -107,14 +110,20 @@ int coda_cnode_make(struct inode **inode, struct CodaFid *fid, struct super_bloc
 }
 
 
+/* Although we treat Coda file identifiers as immutable, there is one
+ * special case for files created during a disconnection where they may
+ * not be globally unique. When an identifier collision is detected we
+ * first try to flush the cached inode from the kernel and finally
+ * resort to renaming/rehashing in-place. Userspace remembers both old
+ * and new values of the identifier to handle any in-flight upcalls.
+ * The real solution is to use globally unique UUIDs as identifiers, but
+ * retrofitting the existing userspace code for this is non-trivial. */
 void coda_replace_fid(struct inode *inode, struct CodaFid *oldfid, 
 		      struct CodaFid *newfid)
 {
-	struct coda_inode_info *cii;
+	struct coda_inode_info *cii = ITOC(inode);
 	unsigned long hash = coda_f2i(newfid);
 	
-	cii = ITOC(inode);
-
 	BUG_ON(!coda_fideq(&cii->c_fid, oldfid));
 
 	/* replace fid and rehash inode */