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@xxxxxxxxxxxxxxxxxxxxx> 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
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