Jeff Layton <[email protected]> wrote:
> On Fri, 2021-06-11 at 10:14 -0400, Andrew W Elble wrote:
> > We're seeing file corruption while running 5.10, bisected to 1cc1699070bd:
> >
> > > > +static int ceph_write_begin(struct file *file, struct address_space
> > > > *mapping,
> > > > + loff_t pos, unsigned len, unsigned flags,
> > > > + struct page **pagep, void **fsdata)
> >
> > <snip>
> >
> > > > + /*
> > > > + * In some cases we don't need to read at all:
> > > > + * - full page write
> > > > + * - write that lies completely beyond EOF
> > > > + * - write that covers the the page from start to EOF
> > > > or beyond it
> > > > + */
> > > > + if ((pos_in_page == 0 && len == PAGE_SIZE) ||
> > > > + (pos >= i_size_read(inode)) ||
> >
> > Shouldn't this be '((pos & PAGE_MASK) >= i_size_read(inode)) ||' ?
> >
> > Seems like fs/netfs/read_helper.c currently has the same issue?
That's not quite right either. page may be larger than PAGE_MASK if
grab_cache_page_write_begin() returns a THP (if that's possible).
Maybe:
(pos & thp_size(page) - 1) >= i_size_read(inode)
Really, we want something like thp_pos(). Maybe Willy has something like that
up his sleeve.
In fact, in netfs_write_begin(), index and pos_in_page should be calculated
after grab_cache_page_write_begin() has been called, just in case the new page
extends before the page containing the requested position.
David
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