linux-kernel - [PATCH 07/10] afs: Fix where page->private is set during write

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Message-ID: <160380664783.3467511.6933796884685103590.stgit@warthog.procyon.org.uk>
Date:   Tue, 27 Oct 2020 13:50:47 +0000
From:   David Howells <dhowells@...hat.com>
To:     linux-afs@...ts.infradead.org
Cc:     dhowells@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 07/10] afs: Fix where page->private is set during write

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@...hat.com>
---

 fs/afs/write.c |   41 +++++++++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 14 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 16a896096ccf..5ed5df906744 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -135,22 +135,8 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
 		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 (!TestSetPagePrivate(page))
-		get_page(page);
-	set_page_private(page, priv);
 	*_page = page;
 	_leave(" = 0");
 	return 0;
@@ -184,6 +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;
 
@@ -215,6 +204,30 @@ 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;
+		trace_afs_page_dirty(vnode, tracepoint_string("dirty+"),
+				     page->index, priv);
+	} else {
+		SetPagePrivate(page);
+		get_page(page);
+		f = from;
+		t = to;
+		priv = (unsigned long)t << AFS_PRIV_SHIFT;
+		priv |= f;
+		trace_afs_page_dirty(vnode, tracepoint_string("dirty"),
+				     page->index, priv);
+	}
+
+	set_page_private(page, priv);
 	set_page_dirty(page);
 	if (PageDirty(page))
 		_debug("dirtied");