NFS/pnfs: Fix a live lock between recalled layouts and layoutget

When the server is recalling a layout, we should ignore the count of
outstanding layoutget calls, since the server is expected to return
either NFS4ERR_RECALLCONFLICT or NFS4ERR_RETURNCONFLICT for as long as
the recall is outstanding.
Currently, we may end up livelocking, causing the layout to eventually
be forcibly revoked.

Fixes: bf0291d ("pNFS: Ensure LAYOUTGET and LAYOUTRETURN are properly serialised")
Cc: [email protected]
Signed-off-by: Trond Myklebust <[email protected]>

Author: Trond Myklebust

fs/nfs/pnfs.c

@@ -1308,7 +1308,7 @@ pnfs_prepare_layoutreturn(struct pnfs_layout_hdr *lo,
 		enum pnfs_iomode *iomode)
 {
 	/* Serialise LAYOUTGET/LAYOUTRETURN */
-	if (atomic_read(&lo->plh_outstanding) != 0)
+	if (atomic_read(&lo->plh_outstanding) != 0 && lo->plh_return_seq == 0)
 		return false;
 	if (test_and_set_bit(NFS_LAYOUT_RETURN_LOCK, &lo->plh_flags))
 		return false;