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, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>