Mel Gorman <mgorman@xxxxxxx> writes: > This reverts the patch "hugetlb: avoid taking i_mmap_mutex in > unmap_single_vma() for hugetlb" from mmotm. > > This patch is possibly a mistake and blocks the merging of a hugetlb fix > where page tables can get corrupted (https://lkml.org/lkml/2012/7/24/93). > The motivation of the patch appears to be two-fold. > > First, it believes that the i_mmap_mutex is to protect against list > corruption of the page->lru lock but that is not quite accurate. The > i_mmap_mutex for shared page tables is meant to protect against races > when sharing and unsharing the page tables. For example, an important > use of i_mmap_mutex is to stabilise the page_count of the PMD page > during huge_pmd_unshare. I missed that. > > Second, it is protecting against a potential deadlock when > unmap_unsingle_page is called from unmap_mapping_range(). However, hugetlbfs > should never be in this path. It has its own setattr and truncate handlers > where are the paths that use unmap_mapping_range(). I noted this in http://article.gmane.org/gmane.linux.kernel.mm/80065 > > Unless Aneesh has another reason for the patch, it should be reverted > to preserve hugetlb page sharing locking. > I guess we want to take this patch as a revert patch rather than dropping the one in -mm. That would help in documenting the i_mmap_mutex locking details in commit message. Or may be we should add necessary comments around the locking ? Acked-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > --- > mm/memory.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 8a989f1..22bc695 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1344,8 +1344,11 @@ static void unmap_single_vma(struct mmu_gather *tlb, > * Since no pte has actually been setup, it is > * safe to do nothing in this case. > */ > - if (vma->vm_file) > + if (vma->vm_file) { > + mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex); > __unmap_hugepage_range(tlb, vma, start, end, NULL); > + mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex); > + } > } else > unmap_page_range(tlb, vma, start, end, details); > } > -- > 1.7.9.2 -- 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>