On 2022/9/15 6:18, Mike Kravetz wrote: > With the new hugetlb vma lock in place, it can also be used to handle > page fault races with file truncation. The lock is taken at the > beginning of the code fault path in read mode. During truncation, it > is taken in write mode for each vma which has the file mapped. The > file's size (i_size) is modified before taking the vma lock to unmap. > > How are races handled? > > The page fault code checks i_size early in processing after taking the > vma lock. If the fault is beyond i_size, the fault is aborted. If the > fault is not beyond i_size the fault will continue and a new page will > be added to the file. It could be that truncation code modifies i_size > after the check in fault code. That is OK, as truncation code will soon > remove the page. The truncation code will wait until the fault is > finished, as it must obtain the vma lock in write mode. As previous thread [1] points out, if vma->vm_private_data is NULL, there won't be any synchronization which provides the same type of synchronization around i_size as provided by the fault mutex as in [2]. ([2] will take the fault mutex for EVERY index in the truncated range) [1] https://lore.kernel.org/lkml/YyOKIhygl66cG8Yr@monkey/T/#m6b69af9e8cdba01246c2b210bd044bf895b815ee [2] https://lore.kernel.org/lkml/20220824175757.20590-5-mike.kravetz@xxxxxxxxxx/ Except from that, this patch looks good to me. Thanks Mike. Thanks, Miaohe Lin
