Messages in this thread | | | Date | Tue, 27 Mar 2012 14:38:15 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 01/19] mm: Make default vm_ops provide ->page_mkwrite handler |
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On Tue, 27 Mar 2012 09:55:27 +0200 Jan Kara <jack@suse.cz> wrote:
> On Fri 23-03-12 15:45:02, Andrew Morton wrote: > > On Mon, 5 Mar 2012 17:00:59 +0100 > > Jan Kara <jack@suse.cz> wrote: > > > > > --- a/mm/filemap.c > > > +++ b/mm/filemap.c > > > @@ -1759,8 +1759,28 @@ page_not_uptodate: > > > } > > > EXPORT_SYMBOL(filemap_fault); > > > > > > +int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) > > > +{ > > > + struct page *page = vmf->page; > > > + struct inode *inode = vma->vm_file->f_path.dentry->d_inode; > > > + int ret = VM_FAULT_LOCKED; > > > + > > > + file_update_time(vma->vm_file); > > > + lock_page(page); > > > + if ((page->mapping != inode->i_mapping) || > > > + (page_offset(page) > i_size_read(inode))) { > > > > Would benefit from a comment explaining how the page can come to be > > outside i_size, and why we fail in that case.
This?
> > I don't think i_mutex is held here, so this test is rather meaningless > > and racy anyway? > i_size test is racy if that's what you mean by "this test". Just I did > the test this way because it's like this in other places and I figured > truncate_pagecache() can take relatively long time so the test has some > effect. But if you think it's not worth it, I can remove it.
It bugs me when we copy-n-paste code without remembering why we had it there in the first place :( iirc, mmapped pages outside i_size can and do happen in some race situations, and are benign. But it's several years since I thought about it and all the details have evaporated and it would take a lot of work to reinstantiate it all. argh.
Also, it's off-by-one, isn't it? Should be page_offset(page) >= i_size?
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