lkml.org 
[lkml]   [2013]   [Dec]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 03/14] mm, hugetlb: protect region tracking via newly introduced resv_map lock
On Mon, Dec 23, 2013 at 10:05:17AM +0900, Joonsoo Kim wrote:
> On Sun, Dec 22, 2013 at 12:58:19AM +1100, David Gibson wrote:
> > On Wed, Dec 18, 2013 at 03:53:49PM +0900, Joonsoo Kim wrote:
> > > There is a race condition if we map a same file on different processes.
> > > Region tracking is protected by mmap_sem and hugetlb_instantiation_mutex.
> > > When we do mmap, we don't grab a hugetlb_instantiation_mutex, but,
> > > grab a mmap_sem. This doesn't prevent other process to modify region
> > > structure, so it can be modified by two processes concurrently.
> > >
> > > To solve this, I introduce a lock to resv_map and make region manipulation
> > > function grab a lock before they do actual work. This makes region
> > > tracking safe.
> >
> > It's not clear to me if you're saying there is a list corruption race
> > bug in the existing code, or only that there will be if the
> > instantiation mutex goes away.
>
> Hello,
>
> The race exists in current code.
> Currently, region tracking is protected by either down_write(&mm->mmap_sem) or
> down_read(&mm->mmap_sem) + instantiation mutex. But if we map this hugetlbfs
> file to two different processes, holding a mmap_sem doesn't have any impact on
> the other process and concurrent access to data structure is possible.

Ouch. In that case:

Acked-by: David Gibson <david@gibson.dropbear.id.au>

It would be really nice to add a testcase for this race to the
libhugetlbfs testsuite.

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2013-12-24 13:41    [W:0.063 / U:0.840 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site