[PATCH 1/2] NFS: Fix deadlocks in nfs_scan_commit_list()

[PATCH 1/2] NFS: Fix deadlocks in nfs_scan_commit_list()

[trondmy]

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

[PATCH 2/2] NFS: Fix up commit deadlocks

[trondmy]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

If O_DIRECT bumps the commit_info rpcs_out field, then that could lead
to fsync() hangs. The fix is to ensure that O_DIRECT calls
nfs_commit_end().

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/direct.c        | 2 +-
 fs/nfs/pnfs_nfs.c      | 2 --
 fs/nfs/write.c         | 9 ++++++---
 include/linux/nfs_fs.h | 1 +
 4 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 2e894fec036b..3c0335c15a73 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -620,7 +620,7 @@ static void nfs_direct_commit_complete(struct nfs_commit_data *data)
 		nfs_unlock_and_release_request(req);
 	}
 
-	if (atomic_dec_and_test(&cinfo.mds->rpcs_out))
+	if (nfs_commit_end(cinfo.mds))
 		nfs_direct_write_complete(dreq);
 }
 
diff --git a/fs/nfs/pnfs_nfs.c b/fs/nfs/pnfs_nfs.c
index 02bd6e83961d..316f68f96e57 100644
--- a/fs/nfs/pnfs_nfs.c
+++ b/fs/nfs/pnfs_nfs.c
@@ -468,7 +468,6 @@ pnfs_bucket_alloc_ds_commits(struct list_head *list,
 				goto out_error;
 			data->ds_commit_index = i;
 			list_add_tail(&data->list, list);
-			atomic_inc(&cinfo->mds->rpcs_out);
 			nreq++;
 		}
 		mutex_unlock(&NFS_I(cinfo->inode)->commit_mutex);
@@ -520,7 +519,6 @@ pnfs_generic_commit_pagelist(struct inode *inode, struct list_head *mds_pages,
 		data->ds_commit_index = -1;
 		list_splice_init(mds_pages, &data->pages);
 		list_add_tail(&data->list, &list);
-		atomic_inc(&cinfo->mds->rpcs_out);
 		nreq++;
 	}
 
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 38f181e1343a..465220f47142 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1673,10 +1673,13 @@ static void nfs_commit_begin(struct nfs_mds_commit_info *cinfo)
 	atomic_inc(&cinfo->rpcs_out);
 }
 
-static void nfs_commit_end(struct nfs_mds_commit_info *cinfo)
+bool nfs_commit_end(struct nfs_mds_commit_info *cinfo)
 {
-	if (atomic_dec_and_test(&cinfo->rpcs_out))
+	if (atomic_dec_and_test(&cinfo->rpcs_out)) {
 		wake_up_var(&cinfo->rpcs_out);
+		return true;
+	}
+	return false;
 }
 
 void nfs_commitdata_release(struct nfs_commit_data *data)
@@ -1776,6 +1779,7 @@ void nfs_init_commit(struct nfs_commit_data *data,
 	data->res.fattr   = &data->fattr;
 	data->res.verf    = &data->verf;
 	nfs_fattr_init(&data->fattr);
+	nfs_commit_begin(cinfo->mds);
 }
 EXPORT_SYMBOL_GPL(nfs_init_commit);
 
@@ -1822,7 +1826,6 @@ nfs_commit_list(struct inode *inode, struct list_head *head, int how,
 
 	/* Set up the argument struct */
 	nfs_init_commit(data, head, NULL, cinfo);
-	atomic_inc(&cinfo->mds->rpcs_out);
 	if (NFS_SERVER(inode)->nfs_client->cl_minorversion)
 		task_flags = RPC_TASK_MOVEABLE;
 	return nfs_initiate_commit(NFS_CLIENT(inode), data, NFS_PROTO(inode),
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 5893b986fa3b..140187b57db8 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -574,6 +574,7 @@ extern int nfs_wb_page_cancel(struct inode *inode, struct page* page);
 extern int  nfs_commit_inode(struct inode *, int);
 extern struct nfs_commit_data *nfs_commitdata_alloc(bool never_fail);
 extern void nfs_commit_free(struct nfs_commit_data *data);
+bool nfs_commit_end(struct nfs_mds_commit_info *cinfo);
 
 static inline int
 nfs_have_writebacks(struct inode *inode)
-- 
2.31.1