Re: [PATCH v2 9/9] hugetlb: clean up code checking for fault/truncation races

Mike Kravetz
2022-09-19T23:32:59Z

On 09/14/22 15:18, 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.
>
> This patch cleans up/removes late checks in the fault paths that try to
> back out pages racing with truncation. As noted above, we just let the
> truncation code remove the pages.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
> fs/hugetlbfs/inode.c | 31 ++++++++++++-------------------
> mm/hugetlb.c | 27 ++++++---------------------
> 2 files changed, 18 insertions(+), 40 deletions(-)

This patch introduced a compiler warning addressed here,

https://lore.kernel.org/linux-mm/Yyj7HsJWfHDoU24U@monkey/

--
Mike Kravetz