On Tuesday, January 17, 2017 2:04 AM Andrea Arcangeli wrote: > > Use the non atomic version of __SetPageUptodate while the page is > still private and not visible to lookup operations. Using the non > atomic version after the page is already visible to lookups is unsafe > as there would be concurrent lock_page operation modifying the > page->flags while it runs. > > This solves a lockup in find_lock_entry with the userfaultfd_shmem > selftest. > > userfaultfd_shm D14296 691 1 0x00000004 > Call Trace: > ? __schedule+0x311/0xb60 > schedule+0x3d/0x90 > schedule_timeout+0x228/0x420 > ? mark_held_locks+0x71/0x90 > ? ktime_get+0x134/0x170 > ? kvm_clock_read+0x25/0x30 > ? kvm_clock_get_cycles+0x9/0x10 > ? ktime_get+0xd6/0x170 > ? __delayacct_blkio_start+0x1f/0x30 > io_schedule_timeout+0xa4/0x110 > ? trace_hardirqs_on+0xd/0x10 > __lock_page+0x12d/0x170 > ? add_to_page_cache_lru+0xe0/0xe0 > find_lock_entry+0xa4/0x190 > shmem_getpage_gfp+0xb9/0xc30 > ? alloc_set_pte+0x56e/0x610 > ? radix_tree_next_chunk+0xf6/0x2d0 > shmem_fault+0x70/0x1c0 > ? filemap_map_pages+0x3bd/0x530 > __do_fault+0x21/0x150 > handle_mm_fault+0xec9/0x1490 > __do_page_fault+0x20d/0x520 > trace_do_page_fault+0x61/0x270 > do_async_page_fault+0x19/0x80 > async_page_fault+0x25/0x30 > > Reported-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> > --- Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> > mm/shmem.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index b1ecd07..873b847 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2247,6 +2247,7 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, > VM_BUG_ON(PageLocked(page) || PageSwapBacked(page)); > __SetPageLocked(page); > __SetPageSwapBacked(page); > + __SetPageUptodate(page); > > ret = mem_cgroup_try_charge(page, dst_mm, gfp, &memcg, false); > if (ret) > @@ -2271,8 +2272,6 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, > if (!pte_none(*dst_pte)) > goto out_release_uncharge_unlock; > > - __SetPageUptodate(page); > - > lru_cache_add_anon(page); > > spin_lock(&info->lock); -- 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>