gfs2: fix an oops in gfs2_permission

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@zeniv.linux.org.uk>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index 2880d6c..697f950 100644 (file)
--- 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 3141db7..dd2720a 100644 (file)
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1540,7 +1540,7 @@ out:
                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);
        }
 }