Patch "gfs2: fix an oops in gfs2_permission" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    gfs2: fix an oops in gfs2_permission

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     gfs2-fix-an-oops-in-gfs2_permission.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 02e9b180800cd3f2701489509e755b28bc32d460
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date:   Mon Oct 2 03:33:44 2023 +0100

    gfs2: fix an oops in gfs2_permission
    
    [ Upstream commit 0abd1557e21c617bd13fc18f7725fc6363c05913 ]
    
    In RCU mode, we might race with gfs2_evict_inode(), which zeroes
    ->i_gl.  Freeing of the object it points to is RCU-delayed, so
    if we manage to fetch the pointer before it's been replaced with
    NULL, we are fine.  Check if we'd fetched NULL and treat that
    as "bail out and tell the caller to get out of RCU mode".
    
    Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
    Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index 0eac045079047..eb4bbe1728c06 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -1868,14 +1868,21 @@ int gfs2_permission(struct mnt_idmap *idmap, struct inode *inode,
 {
 	struct gfs2_inode *ip;
 	struct gfs2_holder i_gh;
+	struct gfs2_glock *gl;
 	int error;
 
 	gfs2_holder_mark_uninitialized(&i_gh);
 	ip = GFS2_I(inode);
-	if (gfs2_glock_is_locked_by_me(ip->i_gl) == NULL) {
+	gl = rcu_dereference(ip->i_gl);
+	if (unlikely(!gl)) {
+		/* inode is getting torn down, must be RCU mode */
+		WARN_ON_ONCE(!(mask & MAY_NOT_BLOCK));
+		return -ECHILD;
+        }
+	if (gfs2_glock_is_locked_by_me(gl) == NULL) {
 		if (mask & MAY_NOT_BLOCK)
 			return -ECHILD;
-		error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
+		error = gfs2_glock_nq_init(gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
 		if (error)
 			return error;
 	}
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 02d93da21b2b0..0dd5641990b90 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1550,7 +1550,7 @@ static void gfs2_evict_inode(struct inode *inode)
 		wait_on_bit_io(&ip->i_flags, GIF_GLOP_PENDING, TASK_UNINTERRUPTIBLE);
 		gfs2_glock_add_to_lru(ip->i_gl);
 		gfs2_glock_put_eventually(ip->i_gl);
-		ip->i_gl = NULL;
+		rcu_assign_pointer(ip->i_gl, NULL);
 	}
 }