releases/5.9.5/afs-fix-where-page-private-is-set-during-write.patch

From e383edb03ba16ca346eabbd4a20efa730f291530 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 26 Oct 2020 14:05:33 +0000
Subject: afs: Fix where page->private is set during write

From: David Howells <dhowells@redhat.com>

[ Upstream commit f792e3ac82fe2c6c863e93187eb7ddfccab68fa7 ]

In afs, page->private is set to indicate the dirty region of a page.  This
is done in afs_write_begin(), but that can't take account of whether the
copy into the page actually worked.

Fix this by moving the change of page->private into afs_write_end().

Fixes: 4343d00872e1 ("afs: Get rid of the afs_writeback record")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/afs/write.c | 41 ++++++++++++++++++++++++++---------------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 7fae9f8b38eb3..f28d85c38cd89 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -135,23 +135,8 @@ try_again:
 		if (!test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags) &&
 		    (to < f || from > t))
 			goto flush_conflicting_write;
-		if (from < f)
-			f = from;
-		if (to > t)
-			t = to;
-	} else {
-		f = from;
-		t = to;
 	}
 
-	priv = (unsigned long)t << AFS_PRIV_SHIFT;
-	priv |= f;
-	trace_afs_page_dirty(vnode, tracepoint_string("begin"),
-			     page->index, priv);
-	if (PagePrivate(page))
-		set_page_private(page, priv);
-	else
-		attach_page_private(page, (void *)priv);
 	*_page = page;
 	_leave(" = 0");
 	return 0;
@@ -185,6 +170,9 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 {
 	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
 	struct key *key = afs_file_key(file);
+	unsigned long priv;
+	unsigned int f, from = pos & (PAGE_SIZE - 1);
+	unsigned int t, to = from + copied;
 	loff_t i_size, maybe_i_size;
 	int ret;
 
@@ -216,6 +204,29 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 		SetPageUptodate(page);
 	}
 
+	if (PagePrivate(page)) {
+		priv = page_private(page);
+		f = priv & AFS_PRIV_MAX;
+		t = priv >> AFS_PRIV_SHIFT;
+		if (from < f)
+			f = from;
+		if (to > t)
+			t = to;
+		priv = (unsigned long)t << AFS_PRIV_SHIFT;
+		priv |= f;
+		set_page_private(page, priv);
+		trace_afs_page_dirty(vnode, tracepoint_string("dirty+"),
+				     page->index, priv);
+	} else {
+		f = from;
+		t = to;
+		priv = (unsigned long)t << AFS_PRIV_SHIFT;
+		priv |= f;
+		attach_page_private(page, (void *)priv);
+		trace_afs_page_dirty(vnode, tracepoint_string("dirty"),
+				     page->index, priv);
+	}
+
 	set_page_dirty(page);
 	if (PageDirty(page))
 		_debug("dirtied");
-- 
2.27.0