fs: don't use igrab() while holding i_lock

Fix the incorrect use of igrab() inside the i_lock in NFS and Ceph‥

If we are already holding the i_lock, we have a reference to the
inode so we can safely use ihold() to gain an extra reference. This
avoids hangs due to lock recursion on the i_lock now that the
inode_lock is gone and igrab() uses the i_lock itself.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: Ryan Mallon <ryan@bluewatersys.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 5 insertions, 4 deletions

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 561438b6a50c..37368ba2e67c 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -92,7 +92,7 @@ static int ceph_set_page_dirty(struct page *page)
                 ci->i_head_snapc = ceph_get_snap_context(snapc);
         ++ci->i_wrbuffer_ref_head;
         if (ci->i_wrbuffer_ref == 0)
-                igrab(inode);
+                ihold(inode);
         ++ci->i_wrbuffer_ref;
         dout("%p set_page_dirty %p idx %lu head %d/%d -> %d/%d "
              "snapc %p seq %lld (%d snaps)\n",
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index f40b9139e437..0aee66b92af3 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -463,8 +463,8 @@ void ceph_queue_cap_snap(struct ceph_inode_info *ci)
 
                 dout("queue_cap_snap %p cap_snap %p queuing under %p\n", inode,
                      capsnap, snapc);
-                igrab(inode);
-                
+                ihold(inode);
+
                 atomic_set(&capsnap->nref, 1);
                 capsnap->ci = ci;
                 INIT_LIST_HEAD(&capsnap->ci_item);
diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index ab1bf5bb021f..a6804f704d9d 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -590,7 +590,8 @@ nfs4_get_open_state(struct inode *inode, struct nfs4_state_owner *owner)
                 state->owner = owner;
                 atomic_inc(&owner->so_count);
                 list_add(&state->inode_states, &nfsi->open_states);
-                state->inode = igrab(inode);
+                ihold(inode);
+                state->inode = inode;
                 spin_unlock(&inode->i_lock);
                 /* Note: The reclaim code dictates that we add stateless
                  * and read-only stateids to the end of the list */