[linux-cifs-client] Re: fsx-linux failing with latest cifs-2.6 git tree

[Jeff Layton]

On Sat, 22 Nov 2008 14:27:44 -0600
Dave Kleikamp <shaggy at linux.vnet.ibm.com> wrote:

> Just took a real quick look, but I have one comment.  I'd leave the page
> alone if it's already PageUptodate.  I wouldn't bother setting
> PageChecked and let cifs_write_end leave it alone when its already
> uptodate.

Ok, it makes sense not to flip page bits unless we need to. How's this
instead? It also switches the code to use zero_user_segments() instead
of calling kmap/memset directly.

I've dropped Steve's SoB for now since this has morphed quite a bit from
his original patch. Steve, feel free to add it back if you approve.

--------------------[snip]--------------------

From da222d5125ec4095f10e9a4c984b6bd6b0cacf18 Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton at redhat.com>
Date: Sun, 23 Nov 2008 06:54:42 -0500
Subject: [PATCH] cifs: fix regression in cifs_write_begin/cifs_write_end

The conversion to write_begin/write_end interfaces had a bug where we
were passing a bad parameter to cifs_readpage_worker. Rather than
passing the page offset of the start of the write, we needed to pass the
offset of the beginning of the page. This was reliably showing up as
data corruption in the fsx-linux test from LTP.

It also became evident that this code was occasionally doing unnecessary
read calls. Optimize those away by using the PG_checked flag to indicate
that the unwritten part of the page has been initialized.

Signed-off-by: Jeff Layton <jlayton at redhat.com>
---
 fs/cifs/file.c |   68 +++++++++++++++++++++++++++++++++++++++++--------------
 1 files changed, 50 insertions(+), 18 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index b691b89..9114ea5 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1475,7 +1475,10 @@ static int cifs_write_end(struct file *file, struct address_space *mapping,
 	cFYI(1, ("write_end for page %p from pos %lld with %d bytes",
 		 page, pos, copied));
 
-	if (!PageUptodate(page) && copied == PAGE_CACHE_SIZE)
+	if (PageChecked(page)) {
+		SetPageUptodate(page);
+		ClearPageChecked(page);
+	} else if (!PageUptodate(page) && copied == PAGE_CACHE_SIZE)
 		SetPageUptodate(page);
 
 	if (!PageUptodate(page)) {
@@ -2062,39 +2065,68 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
 {
 	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 	loff_t offset = pos & (PAGE_CACHE_SIZE - 1);
+	loff_t page_start = pos & PAGE_MASK;
+	loff_t i_size;
+	struct inode *inode;
+	struct page *page;
+	int rc = 0;
 
 	cFYI(1, ("write_begin from %lld len %d", (long long)pos, len));
 
-	*pagep = __grab_cache_page(mapping, index);
-	if (!*pagep)
-		return -ENOMEM;
+	page = __grab_cache_page(mapping, index);
+	if (!page) {
+		rc = -ENOMEM;
+		goto out;
+	}
 
-	if (PageUptodate(*pagep))
-		return 0;
+	if (PageUptodate(page))
+		goto out;
 
 	/* If we are writing a full page it will be up to date,
 	   no need to read from the server */
 	if (len == PAGE_CACHE_SIZE && flags & AOP_FLAG_UNINTERRUPTIBLE)
-		return 0;
-
-	if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
-		int rc;
+		goto out;
 
-		/* might as well read a page, it is fast enough */
-		rc = cifs_readpage_worker(file, *pagep, &offset);
+	/*
+	 * optimize away the read when we have an oplock, and we're not
+	 * expecting to use any of the data we'd be reading in. That is, when
+	 * the page lies beyond the EOF, or straddles the EOF and the write
+	 * would cover all of the existing data in the file.
+	 */
+	inode = page->mapping->host;
+	if (CIFS_I(inode)->clientCanCacheRead) {
+		i_size = i_size_read(inode);
+		if (page_start >= i_size ||
+		    (offset == 0 && (pos + len) >= i_size)) {
+			zero_user_segments(page, 0, offset, offset + len,
+					   PAGE_CACHE_SIZE);
+			/*
+			 * PageChecked means that the parts of the page to
+			 * which we're not writing are considered up to date.
+			 * Once the write data is copied to the page, it can
+			 * be set uptodate.
+			 */
+			SetPageChecked(page);
+			goto out;
+		}
+	}
 
-		/* we do not need to pass errors back
-		   e.g. if we do not have read access to the file
-		   because cifs_write_end will attempt synchronous writes
-		   -- shaggy */
+	if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
+		/*
+		 * might as well read a page, it is fast enough. If we get
+		 * an error, we don't need to return it. cifs_write_end will
+		 * do a sync write instead since PG_uptodate isn't set.
+		 */
+		cifs_readpage_worker(file, page, &page_start);
 	} else {
 		/* we could try using another file handle if there is one -
 		   but how would we lock it to prevent close of that handle
 		   racing with this read? In any case
 		   this will be written out by write_end so is fine */
 	}
-
-	return 0;
+out:
+	*pagep = page;
+	return rc;
 }
 
 const struct address_space_operations cifs_addr_ops = {
-- 
1.5.5.1