On Tue, Dec 24, 2013 at 11:00:12PM +1100, David Gibson wrote: > 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 <da...@gibson.dropbear.id.au> > > It would be really nice to add a testcase for this race to the > libhugetlbfs testsuite.
Okay! I will add it. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
