The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 113aac6d567bda783af36d08f73bfda47d8e9a40 Mon Sep 17 00:00:00 2001

From: Trond Myklebust trond.myklebust@hammerspace.com Date: Sun, 10 Jan 2021 15:46:06 -0500 Subject: [PATCH] NFS: nfs_delegation_find_inode_server must first reference the superblock

Before referencing the inode, we must ensure that the superblock can be referenced. Otherwise, we can end up with iput() calling superblock operations that are no longer valid or accessible.

Fixes: e39d8a186ed0 ("NFSv4: Fix an Oops during delegation callbacks") Signed-off-by: Trond Myklebust trond.myklebust@hammerspace.com

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c index 816e1427f17e..04bf8066980c 100644 --- a/fs/nfs/delegation.c +++ b/fs/nfs/delegation.c @@ -1011,22 +1011,24 @@ nfs_delegation_find_inode_server(struct nfs_server *server, const struct nfs_fh *fhandle) { struct nfs_delegation *delegation; - struct inode *freeme, *res = NULL; + struct super_block *freeme = NULL; + struct inode *res = NULL;

list_for_each_entry_rcu(delegation, &server->delegations, super_list) { spin_lock(&delegation->lock); if (delegation->inode != NULL && !test_bit(NFS_DELEGATION_REVOKED, &delegation->flags) && nfs_compare_fh(fhandle, &NFS_I(delegation->inode)->fh) == 0) { - freeme = igrab(delegation->inode); - if (freeme && nfs_sb_active(freeme->i_sb)) - res = freeme; + if (nfs_sb_active(server->super)) { + freeme = server->super; + res = igrab(delegation->inode); + } spin_unlock(&delegation->lock); if (res != NULL) return res; if (freeme) { rcu_read_unlock(); - iput(freeme); + nfs_sb_deactive(freeme); rcu_read_lock(); } return ERR_PTR(-EAGAIN);