From: NeilBrown <neilb@suse.com>
Date: Fri, 10 Mar 2017 08:19:32 +1100
Subject: [PATCH] NFS: flush out dirty data on file fput().
Patch-mainline: Not yet, maintainer doesn't believe it is a problem
URL: https://www.spinics.net/lists/linux-nfs/msg62622.html
References: bsc#1021762
Any dirty NFS page holds an s_active reference on the superblock,
because page_private() references an nfs_page, which references an
open context, which references the superblock.
So if there are any dirty pages when the filesystem is unmounted, the
unmount will act like a "lazy" unmount and not call ->kill_sb().
Background write-back can then write out the pages *after* the filesystem
unmount has apparently completed.
This contrasts with other filesystems which do not hold extra s_active
references, so ->kill_sb() is reliably called on unmount, and
generic_shutdown_super() will call sync_filesystem() to flush
everything out before the unmount completes.
When open/write/close is used to modify files, the final close causes
f_op->flush to be called, which flushes all dirty pages. However if
open/mmap/close/modify-memory/unmap is used, dirty pages can remain in
memory after the application has dropped all references to the file.
Fix this by calling vfs_fsync() in nfs_file_release (aka
f_op->release()). This means that on the final unmap of a file, all
changes are flushed, and ensures that when unmount is requested there
will be no dirty pages to delay the final unmount.
Without this patch, it is not safe to stop or disconnect the NFS
server after all clients have unmounted. They need to unmount and
call "sync".
Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: NeilBrown <neilb@suse.com>
---
fs/nfs/file.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -82,6 +82,12 @@ nfs_file_release(struct inode *inode, st
{
dprintk("NFS: release(%pD2)\n", filp);
+ if (filp->f_mode & FMODE_WRITE)
+ /* Ensure dirty mmapped pages are flushed
+ * so there will be no dirty pages to
+ * prevent an unmount from completing.
+ */
+ vfs_fsync(filp, 0);
nfs_inc_stats(inode, NFSIOS_VFSRELEASE);
nfs_file_clear_open_context(filp);
return 0;