On Fri, 2005-03-04 at 16:23, Andrew Morton wrote:
> Badari Pulavarty <[EMAIL PROTECTED]> wrote:
> >
> > @@ -1646,13 +1659,34 @@ static int ext3_block_truncate_page(hand
> > unsigned blocksize, iblock, length, pos;
> > struct inode *inode = mapping->host;
> > struct buffer_head *bh;
> > - int err;
> > + int err = 0;
> > void *kaddr;
> >
> > blocksize = inode->i_sb->s_blocksize;
> > length = blocksize - (offset & (blocksize - 1));
> > iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
> >
> > + if (test_opt(inode->i_sb, NOBH) && !page_has_buffers(page)) {
> > + if (!PageUptodate(page)) {
> > + err = mpage_readpage(page, ext3_get_block);
> > + if ((err == 0) && !PageUptodate(page))
> > + wait_on_page_locked(page);
> > + lock_page(page);
> > + }
> > + if (err == 0 && PageUptodate(page)) {
> > + kaddr = kmap_atomic(page, KM_USER0);
> > + memset(kaddr + offset, 0, length);
> > + flush_dcache_page(page);
> > + kunmap_atomic(kaddr, KM_USER0);
> > + set_page_dirty(page);
> > + goto unlock;
> > + }
> > + /*
>
> What's all this doing? (It needs comments please - it's very unobvious).
All its trying to do is - to make sure the page is uptodate so that
it can zero out the portion thats needed.
I can do getblock() and ll_rw_block(READ) instead. I was
trying to re-use the code and mpage_readpage() drops the lock.
What do you think ?
>
> Dropping and reacquiring the page lock in the middle of the truncate there
> is a bit of a worry - need to think about that.
>
> Err, yes, it's buggy - page reclaim can come in, grab the page lock and
> whip the page off the mapping. We end up with an anonymous page and we
> then start trying to write it into the file and all sorts of things.
>
>
> This bit:
>
> if ((err == 0) && !PageUptodate(page))
> wait_on_page_locked(page);
>
> can simply be removed. We're about to lock the page anyway.
Thanks,
Badari
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