From: Trond Myklebust <trond.myklebust@hammerspace.com>
Date: Mon, 4 Oct 2021 15:44:16 -0400
Subject: [PATCH] NFS: Fix deadlocks in nfs_scan_commit_list()
Git-commit: 64a93dbf25d3a1368bb58ddf0f61d0a92d7479e3
Patch-mainline: v5.16-rc1
References: git-fixes

Partially revert commit 2ce209c42c01 ("NFS: Wait for requests that are
locked on the commit list"), since it can lead to deadlocks between
commit requests and nfs_join_page_group().
For now we should assume that any locked requests on the commit list are
either about to be removed and committed by another task, or the writes
they describe are about to be retransmitted. In either case, we should
not need to worry.

Fixes: 2ce209c42c01 ("NFS: Wait for requests that are locked on the commit list")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfs/write.c |   17 ++---------------
 1 file changed, 2 insertions(+), 15 deletions(-)

--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1051,25 +1051,11 @@ nfs_scan_commit_list(struct list_head *s
 	struct nfs_page *req, *tmp;
 	int ret = 0;
 
-restart:
 	list_for_each_entry_safe(req, tmp, src, wb_list) {
 		kref_get(&req->wb_kref);
 		if (!nfs_lock_request(req)) {
-			int status;
-
-			/* Prevent deadlock with nfs_lock_and_join_requests */
-			if (!list_empty(dst)) {
-				nfs_release_request(req);
-				continue;
-			}
-			/* Ensure we make progress to prevent livelock */
-			mutex_unlock(&NFS_I(cinfo->inode)->commit_mutex);
-			status = nfs_wait_on_request(req);
 			nfs_release_request(req);
-			mutex_lock(&NFS_I(cinfo->inode)->commit_mutex);
-			if (status < 0)
-				break;
-			goto restart;
+			continue;
 		}
 		nfs_request_remove_commit_list(req, cinfo);
 		clear_bit(PG_COMMIT_TO_DS, &req->wb_flags);
@@ -1938,6 +1924,7 @@ static int __nfs_commit_inode(struct ino
 	int may_wait = how & FLUSH_SYNC;
 	int ret, nscan;
 
+	how &= ~FLUSH_SYNC;
 	nfs_init_cinfo_from_inode(&cinfo, inode);
 	nfs_commit_begin(cinfo.mds);
 	for (;;) {