pNFS: Prevent the layout header refcount going to zero in pnfs_roc()

Ensure that we hold a reference to the layout header when processing
the pNFS return-on-close so that the refcount value does not inadvertently
go to zero.

Reported-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: stable@vger.kernel.org # v4.10+
Tested-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index c13e826614b5..ee723aa153a3 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -292,8 +292,11 @@ pnfs_detach_layout_hdr(struct pnfs_layout_hdr *lo)
 void
 pnfs_put_layout_hdr(struct pnfs_layout_hdr *lo)
 {
-        struct inode *inode = lo->plh_inode;
+        struct inode *inode;
 
+        if (!lo)
+                return;
+        inode = lo->plh_inode;
         pnfs_layoutreturn_before_put_layout_hdr(lo);
 
         if (refcount_dec_and_lock(&lo->plh_refcount, &inode->i_lock)) {
@@ -1241,10 +1244,12 @@ retry:
         spin_lock(&ino->i_lock);
         lo = nfsi->layout;
         if (!lo || !pnfs_layout_is_valid(lo) ||
-            test_bit(NFS_LAYOUT_BULK_RECALL, &lo->plh_flags))
+            test_bit(NFS_LAYOUT_BULK_RECALL, &lo->plh_flags)) {
+                lo = NULL;
                 goto out_noroc;
+        }
+        pnfs_get_layout_hdr(lo);
         if (test_bit(NFS_LAYOUT_RETURN_LOCK, &lo->plh_flags)) {
-                pnfs_get_layout_hdr(lo);
                 spin_unlock(&ino->i_lock);
                 wait_on_bit(&lo->plh_flags, NFS_LAYOUT_RETURN,
                                 TASK_UNINTERRUPTIBLE);
@@ -1312,10 +1317,12 @@ out_noroc:
                 struct pnfs_layoutdriver_type *ld = NFS_SERVER(ino)->pnfs_curr_ld;
                 if (ld->prepare_layoutreturn)
                         ld->prepare_layoutreturn(args);
+                pnfs_put_layout_hdr(lo);
                 return true;
         }
         if (layoutreturn)
                 pnfs_send_layoutreturn(lo, &stateid, iomode, true);
+        pnfs_put_layout_hdr(lo);
         return false;
 }