On 09/22/23 10:37, Rik van Riel wrote: > On Thu, 2023-09-21 at 15:42 -0700, Mike Kravetz wrote: > > On 09/19/23 22:16, riel@xxxxxxxxxxx wrote: > > > From: Rik van Riel <riel@xxxxxxxxxxx> > > > > > > Extend the locking scheme used to protect shared hugetlb mappings > > > from truncate vs page fault races, in order to protect private > > > hugetlb mappings (with resv_map) against MADV_DONTNEED. > > > > > > Add a read-write semaphore to the resv_map data structure, and > > > use that from the hugetlb_vma_(un)lock_* functions, in preparation > > > for closing the race between MADV_DONTNEED and page faults. > > > > > > Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx> > > > --- > > > include/linux/hugetlb.h | 6 ++++++ > > > mm/hugetlb.c | 36 ++++++++++++++++++++++++++++++++---- > > > 2 files changed, 38 insertions(+), 4 deletions(-) > > > > This looks straight forward. > > > > However, I ran just this patch through libhugetlbfs test suite and it > > hung on > > misaligned_offset (2M: 32). > > https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/misaligned_offset.c > > > Speaking of "looks straightforward", how do I compile the > libhugetlbfs code? > > The __morecore variable, which is pointed at either the > THP or hugetlbfs morecore function, does not seem to be > defined anywhere in the sources. > > Do I need to run some magic script (didn't find it) to > get a special header file set up before I can build > libhugetlbfs? libhugetlbfs is a mess! Distros have dropped it. However, I still find the test cases useful. I have a special VM with an old glibc just for running the tests. Sorry, can't give instructions for using tests on a recent glibc. But, back to this patch ... With the hints from the locking debug code, it came to me on my walk this morning. We need to also have __hugetlb_vma_unlock_write_free() work for private vmas as called from __unmap_hugepage_range_final. This additional change (or something like it) is required in this patch. diff --git a/mm/hugetlb.c b/mm/hugetlb.c index f906c5fa4d09..8f3d5895fffc 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -372,6 +372,11 @@ static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma) struct hugetlb_vma_lock *vma_lock = vma->vm_private_data; __hugetlb_vma_unlock_write_put(vma_lock); + } else if (__vma_private_lock(vma)) { + struct resv_map *resv_map = vma_resv_map(vma); + + /* no free for anon vmas, but still need to unlock */ + up_write(&resv_map->rw_sema); } } -- Mike Kravetz
