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));