On Tue, 20 Oct 2015, Mike Kravetz wrote:
> At page fault time, check i_private which indicates a fallocate hole punch
> is in progress. If the fault falls within the hole, wait for the hole
> punch operation to complete before proceeding with the fault.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
> mm/hugetlb.c | 39 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 39 insertions(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 3c7db92..2a5e9b4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3580,6 +3580,7 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> struct page *pagecache_page = NULL;
> struct hstate *h = hstate_vma(vma);
> struct address_space *mapping;
> + struct inode *inode = file_inode(vma->vm_file);
> int need_wait_lock = 0;
>
> address &= huge_page_mask(h);
> @@ -3603,6 +3604,44 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> idx = vma_hugecache_offset(h, vma, address);
>
> /*
> + * page faults could race with fallocate hole punch. If a page
> + * is faulted between unmap and deallocation, it will still remain
> + * in the punched hole. During hole punch operations, a hugetlb_falloc
> + * structure will be pointed to by i_private. If this fault is for
> + * a page in a hole being punched, wait for the operation to finish
> + * before proceeding.
> + *
> + * Even with this strategy, it is still possible for a page fault to
> + * race with hole punch. In this case, remove_inode_hugepages() will
> + * unmap the page and then remove. Checking i_private as below should
> + * catch most of these races as we want to minimize unmapping a page
> + * multiple times.
> + */
> + if (unlikely(inode->i_private)) {
> + struct hugetlb_falloc *hugetlb_falloc;
> +
> + spin_lock(&inode->i_lock);
> + hugetlb_falloc = inode->i_private;
> + if (hugetlb_falloc && hugetlb_falloc->waitq &&
Not important, but that "&& hugetlb_falloc->waitq " is redundant.
> + idx >= hugetlb_falloc->start &&
> + idx <= hugetlb_falloc->end) {
Not important, but "idx < hugetlb_falloc->end" would be better.
> + wait_queue_head_t *hugetlb_falloc_waitq;
> + DEFINE_WAIT(hugetlb_fault_wait);
> +
> + hugetlb_falloc_waitq = hugetlb_falloc->waitq;
> + prepare_to_wait(hugetlb_falloc_waitq,
> + &hugetlb_fault_wait,
> + TASK_UNINTERRUPTIBLE);
> + spin_unlock(&inode->i_lock);
> + schedule();
> +
> + spin_lock(&inode->i_lock);
> + finish_wait(hugetlb_falloc_waitq, &hugetlb_fault_wait);
> + }
> + spin_unlock(&inode->i_lock);
> + }
> +
> + /*
> * Serialize hugepage allocation and instantiation, so that we don't
> * get spurious allocation failures if two CPUs race to instantiate
> * the same page in the page cache.
> --
> 2.4.3
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