Re: [PATCH v3 03/14] mm, hugetlb: protect region tracking via newlyintroduced resv_map lock

[Joonsoo Kim]

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.

Thanks.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/