On Friday 19 October 2007 17:03, Nick Piggin wrote:
> On Friday 19 October 2007 16:05, Erez Zadok wrote:
> > David,
> >
> > I'm testing unionfs on top of jffs2, using 2.6.24 as of linus's commit
> > 4fa4d23fa20de67df919030c1216295664866ad7. All of my unionfs tests pass
> > when unionfs is stacked on top of jffs2, other than my truncate test --
> > whic tries to truncate files up/down (through the union, which then is
> > passed through to the lower jffs2 f/s). The same truncate test passes on
> > all other file systems I've tried unionfs/2.6.24 with, as well as all of
> > the earlier kernels that unionfs runs on (2.6.9--2.6.23). So I tend to
> > think this bug is more probably due to something else going on in 2.6.24,
> > possibly wrt jffs2/mtd. (Of course, it's still possible that unionfs
> > isn't doing something right -- any pointers?)
> >
> > The oops trace is included below. Is this a known issue and if so, any
> > fixes? If this is the first you hear of this problem, let me know and
> > I'll try to narrow it down further.
>
> It's had quite a lot of recent changes in that area -- the "new aops"
> patches.
>
> They've been getting quite a bit of testing in -mm and no such problems,
> but I doubt anyone was doing much unionfs over jffs2, or even much jffs2
> testing with -mm.
>
> The bug smells like jffs2 is actually passing back a "written" length
> greater than the length we passed into it.
>
> The following might show what's happening.
Hmm, looks like jffs2_write_end is writing more than we actually ask it
to, and returns that back.
unsigned aligned_start = start & ~3;
and
if (end == PAGE_CACHE_SIZE) {
/* When writing out the end of a page, write out the
_whole_ page. This helps to reduce the number of
nodes in files which have many short writes, like
syslog files. */
start = aligned_start = 0;
}
These "longer" writes are fine, but they shouldn't get propagated back
to the vm/vfs. Something like the following patch might fix it.
Index: linux-2.6/fs/jffs2/file.c
===================================================================
--- linux-2.6.orig/fs/jffs2/file.c
+++ linux-2.6/fs/jffs2/file.c
@@ -255,7 +255,7 @@ static int jffs2_write_end(struct file *
_whole_ page. This helps to reduce the number of
nodes in files which have many short writes, like
syslog files. */
- start = aligned_start = 0;
+ aligned_start = 0;
}
ri = jffs2_alloc_raw_inode();
@@ -291,14 +291,11 @@ static int jffs2_write_end(struct file *
}
/* Adjust writtenlen for the padding we did, so we don't confuse our caller */
- if (writtenlen < (start&3))
- writtenlen = 0;
- else
- writtenlen -= (start&3);
+ writtenlen -= min(writtenlen, (start - aligned_start));
if (writtenlen) {
- if (inode->i_size < (pg->index << PAGE_CACHE_SHIFT) + start + writtenlen) {
- inode->i_size = (pg->index << PAGE_CACHE_SHIFT) + start + writtenlen;
+ if (inode->i_size < pos + start + writtenlen) {
+ inode->i_size = pos + start + writtenlen;
inode->i_blocks = (inode->i_size + 511) >> 9;
inode->i_ctime = inode->i_mtime = ITIME(je32_to_cpu(ri->ctime));
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