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

[Jeff Layton]

On Tue, 25 Nov 2008 22:04:04 -0600
"Steve French" <smfrench at gmail.com> wrote:

> Do you know why someone added the AOP_FLAG_UNITERRUPTIBLE check in
> cifs_write_begin instead of always marking a page up to date if we are
> writing the whole page?  How often would that flag be set - I only see
> it in the path which calls generic_file_buffered_write
> 
>  	/* 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)
> 
> It seems restrictive

Given that I now understand what AOP_FLAG_UNINTERRUPTIBLE is supposed
to do, this patch is probably what we need. Running tests on it now.

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

From 366afe94ecfb314f3126bc9a668b6be61469089f Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton at redhat.com>
Date: Wed, 26 Nov 2008 07:01:33 -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 |   80 +++++++++++++++++++++++++++++++++++++++++--------------
 1 files changed, 59 insertions(+), 21 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index b691b89..37567c9 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 +2065,74 @@ 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;
-
-	if (PageUptodate(*pagep))
-		return 0;
+	page = __grab_cache_page(mapping, index);
+	if (!page) {
+		rc = -ENOMEM;
+		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 (PageUptodate(page))
+		goto out;
 
-	if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
-		int rc;
+	/* only optimize away the read if the copy's not interruptible */
+	if (flags & AOP_FLAG_UNINTERRUPTIBLE) {
+		/*
+		 * 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)
+			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 will cover all of the existing data.
+		 */
+		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 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