[PATCH 5.10 10/13] Revert "nfsd4: remove check_conflicting_opens warning"

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: J. Bruce Fields <bfields@redhat.com>

commit 4aa5e002034f0701c3335379fd6c22d7f3338cce upstream.

This reverts commit 50747dd5e47b "nfsd4: remove check_conflicting_opens
warning", as a prerequisite for reverting 94415b06eb8a, which has a
serious bug.

Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/nfsd/nfs4state.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4957,6 +4957,7 @@ static int nfsd4_check_conflicting_opens
 		writes--;
 	if (fp->fi_fds[O_RDWR])
 		writes--;
+	WARN_ON_ONCE(writes < 0);
 	if (writes > 0)
 		return -EAGAIN;
 	spin_lock(&fp->fi_lock);