Re: data loss in 2.6.9-rc1-mm1

[Hugh Dickins]

On Fri, 27 Aug 2004, Denis Vlasenko wrote:
> On Friday 27 August 2004 13:55, Gergely Tamas wrote:
> >
> > I've hit the following data loss problem under 2.6.9-rc1-mm1.
> >
> > If I copy data from a file to another the target will be smaller then
> > the source file.
> >
> > 2.6.9-rc1 does not have this problem
> > 2.6.8.1-mm4 does not have this problem
> > 2.6.9-rc1-mm1 _does have_ this problem
> 
> I've seen some errors from KDE too. Let me do your test...
> 
> # dd if=/dev/zero of=testfile bs=$((1024*1024)) count=10
> 10+0 records in
> 10+0 records out
> # cat testfile > testfile.1
> # ls -l test*
> -rw-r--r--    1 root     root     10485760 Aug 27 14:53 testfile
> -rw-r--r--    1 root     root     10481664 Aug 27 14:53 testfile.1

Hmm, 2.6.9-rc1-mm1 looks like not a release to trust your (page
size multiple) data to!  You should find the patch below fixes it
(and, I hope, the issue the erroneous patches were trying to fix).

Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>

--- 2.6.9-rc1-mm1/mm/filemap.c	2004-08-26 12:09:50.000000000 +0100
+++ linux/mm/filemap.c	2004-08-27 14:35:32.113359872 +0100
@@ -722,10 +722,7 @@ void do_generic_mapping_read(struct addr
 	offset = *ppos & ~PAGE_CACHE_MASK;
 
 	isize = i_size_read(inode);
-	if (!isize)
-		goto out;
-
-	end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
+	end_index = isize >> PAGE_CACHE_SHIFT;
 
 	for (;;) {
 		struct page *page;
@@ -733,6 +730,11 @@ void do_generic_mapping_read(struct addr
 
 		if (index > end_index)
 			goto out;
+		if (index == end_index) {
+			nr = isize & ~PAGE_CACHE_MASK;
+			if (nr <= offset)
+				goto out;
+		}
 
 		cond_resched();
 		page_cache_readahead(mapping, &ra, filp, index);
@@ -831,8 +833,8 @@ readpage:
 		 * another truncate extends the file - this is desired though).
 		 */
 		isize = i_size_read(inode);
-		end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
-		if (unlikely(!isize || index > end_index)) {
+		end_index = isize >> PAGE_CACHE_SHIFT;
+		if (unlikely(index > end_index)) {
 			page_cache_release(page);
 			goto out;
 		}

-
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