On Wed, Jan 04, 2012 at 03:06:43PM +0900, Takuya Yoshikawa wrote: > It is possible that the __set_bit() in mark_page_dirty() is called > simultaneously on the same region of memory, which may result in only > one bit being set, because some callers do not take mmu_lock before > mark_page_dirty(). > > This problem is hard to produce because when we reach mark_page_dirty() > beginning from, e.g., tdp_page_fault(), mmu_lock is being held during > __direct_map(): making kvm-unit-tests' dirty log api test write to two > pages concurrently was not useful for this reason. > > So we have confirmed that there can actually be race condition by > checking if some callers really reach there without holding mmu_lock > using spin_is_locked(): probably they were from kvm_write_guest_page(). > > To fix this race, this patch changes the bit operation to the atomic > version: note that nr_dirty_pages also suffers from the race but we do > not need exactly correct numbers for now. > > Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx> Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
