Subject: Re: [RFC][PATCHES] iov_iter.c rewrite

From: Al Viro <[email-masked]>
Date: Mon, 8 Dec 2014 17:58:05 +0000

On Mon, Dec 08, 2014 at 06:46:50PM +0200, Kirill A. Shutemov wrote:

> I guess this crash is related to the patchset.

Might be.  Do you have a reproducer for it?

It looks like the second VIRTUAL_BUG_ON() in __phys_addr(), most likely
from __pa(), from virt_to_page(), from
                unsigned long addr = (unsigned long)v.iov_base, end;
                size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));

                if (len > maxpages * PAGE_SIZE)
                        len = maxpages * PAGE_SIZE;
                addr &= ~(PAGE_SIZE - 1);
                for (end = addr + len; addr < end; addr += PAGE_SIZE)
                        get_page(*pages++ = virt_to_page(addr));
                return len - *start;
in iov_iter_get_pages().  And that's ITER_KVEC case there...  Further
call chain looks like dio_refill_pages(), from dio_get_page(), from
do_direct_io(), eventually from kernel_read() and finit_module(),
Presumably called on O_DIRECT descriptor...

I'll try to reproduce it here, but if you have any reliable reproducer, it
would be very welcome (and would make a useful addition to LTP and/or
xfstests).