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

From: Al Viro
Date: Mon Dec 08 2014 - 12:58:15 EST

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
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