gfs2: Fix gfs2_lookup_by_inum lock inversion

The current gfs2_lookup_by_inum takes the glock of a presumed inode
identified by block number, verifies that the block is indeed an inode,
and then instantiates and reads the new inode via gfs2_inode_lookup.

However, instantiating a new inode may block on freeing a previous
instance of that inode (__wait_on_freeing_inode), and freeing an inode
requires to take the glock already held, leading to lock inversion and
deadlock.

Fix this by first instantiating the new inode, then verifying that the
block is an inode (if required), and then reading in the new inode, all
in gfs2_inode_lookup.

If the block we are looking for is not an inode, we discard the new
inode via iget_failed, which marks inodes as bad and unhashes them.
Other tasks waiting on that inode will get back a bad inode back from
ilookup or iget_locked; in that case, retry the lookup.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 706fd9352f36..ce4637518d3b 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -576,7 +576,7 @@ static void delete_work_func(struct work_struct *work)
 	struct gfs2_glock *gl = container_of(work, struct gfs2_glock, gl_delete);
 	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
 	struct gfs2_inode *ip;
-	struct inode *inode;
+	struct inode *inode = NULL;
 	u64 no_addr = gl->gl_name.ln_number;
 
 	/* If someone's using this glock to create a new dinode, the block must
@@ -590,7 +590,7 @@ static void delete_work_func(struct work_struct *work)
 
 	if (ip)
 		inode = gfs2_ilookup(sdp->sd_vfs, no_addr);
-	else
+	if (IS_ERR_OR_NULL(inode))
 		inode = gfs2_lookup_by_inum(sdp, no_addr, NULL, GFS2_BLKST_UNLINKED);
 	if (inode && !IS_ERR(inode)) {
 		d_prune_aliases(inode);