Commit 9a5cc85c authored by Alistair Popple's avatar Alistair Popple Committed by Linus Torvalds
Browse files

mm/memory.c: allow different return codes for copy_nonpresent_pte() 

Currently if copy_nonpresent_pte() returns a non-zero value it is assumed
to be a swap entry which requires further processing outside the loop in
copy_pte_range() after dropping locks.  This prevents other values being
returned to signal conditions such as failure which a subsequent change
requires.

Instead make copy_nonpresent_pte() return an error code if further
processing is required and read the value for the swap entry in the main
loop under the ptl.

Link: https://lkml.kernel.org/r/20210616105937.23201-7-apopple@nvidia.com


Signed-off-by: default avatarAlistair Popple <apopple@nvidia.com>
Reviewed-by: default avatarPeter Xu <peterx@redhat.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6b49bf6d

mm/memory.c

+17 −11
Original line number Diff line number Diff line
@@ -717,7 +717,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, 


	if (likely(!non_swap_entry(entry))) {

		if (swap_duplicate(entry) < 0)

			return entry.val;

			return -EIO;



		/* make sure dst_mm is on swapoff's mmlist. */

		if (unlikely(list_empty(&dst_mm->mmlist))) {
@@ -973,12 +973,14 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, 
			continue;

		}

		if (unlikely(!pte_present(*src_pte))) {

			entry.val = copy_nonpresent_pte(dst_mm, src_mm,

			ret = copy_nonpresent_pte(dst_mm, src_mm,

						  dst_pte, src_pte,

						  dst_vma, src_vma,

						  addr, rss);

			if (entry.val)

			if (ret == -EIO) {

				entry = pte_to_swp_entry(*src_pte);

				break;

			}

			progress += 8;

			continue;

		}
@@ -1011,20 +1013,24 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, 
	pte_unmap_unlock(orig_dst_pte, dst_ptl);

	cond_resched();



	if (entry.val) {

	if (ret == -EIO) {

		VM_WARN_ON_ONCE(!entry.val);

		if (add_swap_count_continuation(entry, GFP_KERNEL) < 0) {

			ret = -ENOMEM;

			goto out;

		}

		entry.val = 0;

	} else if (ret) {

		WARN_ON_ONCE(ret != -EAGAIN);

	} else if (ret ==  -EAGAIN) {

		prealloc = page_copy_prealloc(src_mm, src_vma, addr);

		if (!prealloc)

			return -ENOMEM;

	} else if (ret) {

		VM_WARN_ON_ONCE(1);

	}



	/* We've captured and resolved the error. Reset, try again. */

	ret = 0;

	}



	if (addr != end)

		goto again;

out: