[PATCH -next,v2 2/3] NFS: nfs{,4}_file_flush() return correct writeback errors

[ChenXiaoSong <chenxiaosong2@huawei.com>]

filemap_sample_wb_err() will return 0 if old wb error have not been consumed,
then filemap_check_wb_err() will return the unchanged old wb error.

Reproducer:
        nfs server            |       nfs client
 -----------------------------|---------------------------------------------
 # No space left on server    |
 fallocate -l 100G /svr/nospc |
                              | mount -t nfs $nfs_server_ip:/ /mnt
                              |
                              | # Expected error: No space left on device
                              | dd if=/dev/zero of=/mnt/file count=1 ibs=10K
                              |
                              | # Release space on mountpoint
                              | rm /mnt/nospc
                              |
                              | # Unexpected error: No space left on device
                              | dd if=/dev/zero of=/mnt/file count=1 ibs=10K

Fix this by detecting writeback error from return value of nfs_wb_all(),
and return the more nuanced error -(file->f_mapping->wb_err & MAX_ERRNO) if
there is new wb error while nfs_wb_all().

Fixes: 67dd23f9e6fb ("nfs: ensure correct writeback errors are returned on close()")
Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
---
 fs/nfs/file.c     | 8 ++++----
 fs/nfs/nfs4file.c | 8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 5513ab63c108..353f1f832519 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -136,7 +136,7 @@ static int
 nfs_file_flush(struct file *file, fl_owner_t id)
 {
 	struct inode	*inode = file_inode(file);
-	errseq_t since;
+	errseq_t error = 0;
 
 	dprintk("NFS: flush(%pD2)\n", file);
 
@@ -145,9 +145,9 @@ nfs_file_flush(struct file *file, fl_owner_t id)
 		return 0;
 
 	/* Flush writes to the server and return any errors */
-	since = filemap_sample_wb_err(file->f_mapping);
-	nfs_wb_all(inode);
-	return filemap_check_wb_err(file->f_mapping, since);
+	if (nfs_wb_all(inode))
+		error = filemap_check_wb_err(file->f_mapping, 0);
+	return error;
 }
 
 ssize_t
diff --git a/fs/nfs/nfs4file.c b/fs/nfs/nfs4file.c
index d258933cf8c8..cbbe66b54417 100644
--- a/fs/nfs/nfs4file.c
+++ b/fs/nfs/nfs4file.c
@@ -111,7 +111,7 @@ static int
 nfs4_file_flush(struct file *file, fl_owner_t id)
 {
 	struct inode	*inode = file_inode(file);
-	errseq_t since;
+	errseq_t error = 0;
 
 	dprintk("NFS: flush(%pD2)\n", file);
 
@@ -127,9 +127,9 @@ nfs4_file_flush(struct file *file, fl_owner_t id)
 		return filemap_fdatawrite(file->f_mapping);
 
 	/* Flush writes to the server and return any errors */
-	since = filemap_sample_wb_err(file->f_mapping);
-	nfs_wb_all(inode);
-	return filemap_check_wb_err(file->f_mapping, since);
+	if (nfs_wb_all(inode))
+		error = filemap_check_wb_err(file->f_mapping, 0);
+	return error;
 }
 
 #ifdef CONFIG_NFS_V4_2
-- 
2.31.1