[PATCH 5/6] gfs2: annotate i_gl with __rcu

ip->i_gl is always set over the lifetime of a gfs2 inode; it is initialized at
inode create time and torn down during evict.

However, gfs2_permission() can be called on an inode in non-blocking mode, when
the inode may already be undergoing evict.  So far, to make that work, we have
been using rcu_dereference_check() in gfs2_permission() and
rcu_assign_pointer() in gfs2_evict_inode().

However, ip->i_gl wasn't marked as __rcu so far.  rcu_dereference_check() and
rcu_assign_pointer() expect __rcu pointer arguments, and sparse complains when
regular pointers are passed to those functions:

fs/gfs2/super.c:1516:17: error: incompatible types in comparison expression (different address spaces):
fs/gfs2/super.c:1516:17:    struct gfs2_glock [noderef] __rcu *
fs/gfs2/super.c:1516:17:    struct gfs2_glock *
fs/gfs2/inode.c:1988:14: error: incompatible types in comparison expression (different address spaces):
fs/gfs2/inode.c:1988:14:    struct gfs2_glock [noderef] __rcu *
fs/gfs2/inode.c:1988:14:    struct gfs2_glock *

To fix those errors, turn ip->i_gl into a __rcu variable.  Use
rcu_assign_pointer() to assign to it, and rcu_dereference_protected() to access
it when the pointer is known to be valid.

Make sure not to use gfs2_inode_glock() in gfs2_permission().

Based on a patch from Adrian Garcia Casado <[email protected]>.

Signed-off-by: Andreas Gruenbacher <[email protected]>
---
 fs/gfs2/incore.h | 4 ++--
 fs/gfs2/inode.c  | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 3ae8e2be486c..0a48f8e8ed6c 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -391,7 +391,7 @@ struct gfs2_inode {
 	u64 i_generation;
 	u64 i_eattr;
 	unsigned long i_flags;		/* GIF_... */
-	struct gfs2_glock *i_gl;
+	struct gfs2_glock __rcu *i_gl;
 	struct gfs2_holder i_iopen_gh;
 	struct gfs2_qadata *i_qadata; /* quota allocation data */
 	struct gfs2_holder i_rgd_gh;
@@ -881,6 +881,6 @@ static inline unsigned gfs2_max_stuffed_size(const struct gfs2_inode *ip)
 
 static inline struct gfs2_glock *gfs2_inode_glock(struct inode *inode)
 {
-       return GFS2_I(inode)->i_gl;
+       return rcu_dereference_protected(GFS2_I(inode)->i_gl, 1);
 }
 #endif /* __INCORE_DOT_H__ */
diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index 5aaed0018fb3..d4e1e443391e 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -151,7 +151,7 @@ struct inode *gfs2_inode_lookup(struct super_block *sb, unsigned int type,
 				       &gl);
 		if (unlikely(error))
 			goto fail;
-		ip->i_gl = gl;
+		rcu_assign_pointer(ip->i_gl, gl);
 
 		error = gfs2_glock_get(sdp, no_addr, &gfs2_iopen_glops, CREATE,
 				       &io_gl);
@@ -244,7 +244,7 @@ struct inode *gfs2_inode_lookup(struct super_block *sb, unsigned int type,
 		gfs2_glock_dq_uninit(&i_gh);
 	if (gl) {
 		gfs2_glock_put(gl);
-		ip->i_gl = NULL;
+		rcu_assign_pointer(ip->i_gl, NULL);
 	}
 	iget_failed(inode);
 	return ERR_PTR(error);
@@ -840,7 +840,7 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
 	error = gfs2_glock_get(sdp, ip->i_no_addr, &gfs2_inode_glops, CREATE, &gl);
 	if (error)
 		goto fail_dealloc_inode;
-	ip->i_gl = gl;
+	rcu_assign_pointer(ip->i_gl, gl);
 
 	error = gfs2_glock_get(sdp, ip->i_no_addr, &gfs2_iopen_glops, CREATE, &io_gl);
 	if (error)
@@ -940,7 +940,7 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
 fail_free_inode:
 	if (gl) {
 		gfs2_glock_put(gl);
-		ip->i_gl = NULL;
+		rcu_assign_pointer(ip->i_gl, NULL);
 	}
 	gfs2_rs_deltree(&ip->i_res);
 	gfs2_qa_put(ip);
-- 
2.55.0