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From:   trondmy@kernel.org
To:     linux-nfs@vger.kernel.org
Subject: [PATCH 1/2] NFS: Fix deadlocks in nfs_scan_commit_list()
Date:   Tue,  5 Oct 2021 12:10:35 -0400
Message-Id: <20211005161036.1054428-1-trondmy@kernel.org>
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From: Trond Myklebust <trond.myklebust@hammerspace.com>

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

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index b89d5ef3af0e..38f181e1343a 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1039,25 +1039,11 @@ nfs_scan_commit_list(struct list_head *src, struct list_head *dst,
 	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);
@@ -1952,6 +1938,7 @@ static int __nfs_commit_inode(struct inode *inode, int how,
 	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 (;;) {
-- 
2.31.1