+ mm-memoryc-allow-different-return-codes-for-copy_nonpresent_pte.patch added to -mm tree

* + mm-memoryc-allow-different-return-codes-for-copy_nonpresent_pte.patch added to -mm tree
@ 2021-06-16 23:37 akpm
  0 siblings, 0 replies; 2+ messages in thread
From: akpm @ 2021-06-16 23:37 UTC (permalink / raw)
  To: apopple, bskeggs, hch, hughd, jgg, jhubbard, mm-commits, peterx,
	rcampbell, shakeelb, willy


The patch titled
     Subject: mm/memory.c: allow different return codes for copy_nonpresent_pte()
has been added to the -mm tree.  Its filename is
     mm-memoryc-allow-different-return-codes-for-copy_nonpresent_pte.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-memoryc-allow-different-return-codes-for-copy_nonpresent_pte.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-memoryc-allow-different-return-codes-for-copy_nonpresent_pte.patch

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------------------------------------------------------
From: Alistair Popple <apopple@nvidia.com>
Subject: 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: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Peter 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: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory.c |   28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

--- a/mm/memory.c~mm-memoryc-allow-different-return-codes-for-copy_nonpresent_pte
+++ a/mm/memory.c
@@ -717,7 +717,7 @@ copy_nonpresent_pte(struct mm_struct *ds
 
 	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 @@ again:
 			continue;
 		}
 		if (unlikely(!pte_present(*src_pte))) {
-			entry.val = copy_nonpresent_pte(dst_mm, src_mm,
-							dst_pte, src_pte,
-							dst_vma, src_vma,
-							addr, rss);
-			if (entry.val)
+			ret = copy_nonpresent_pte(dst_mm, src_mm,
+						  dst_pte, src_pte,
+						  dst_vma, src_vma,
+						  addr, rss);
+			if (ret == -EIO) {
+				entry = pte_to_swp_entry(*src_pte);
 				break;
+			}
 			progress += 8;
 			continue;
 		}
@@ -1011,20 +1013,24 @@ again:
 	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;
-		/* We've captured and resolved the error. Reset, try again. */
-		ret = 0;
+	} 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:
_

Patches currently in -mm which might be from apopple@nvidia.com are

mm-remove-special-swap-entry-functions.patch
mm-swapops-rework-swap-entry-manipulation-code.patch
mm-rmap-split-try_to_munlock-from-try_to_unmap.patch
mm-rmap-split-migration-into-its-own-function.patch
mm-rename-migrate_pgmap_owner.patch
mm-memoryc-allow-different-return-codes-for-copy_nonpresent_pte.patch
mm-device-exclusive-memory-access.patch
mm-selftests-for-exclusive-device-memory.patch
nouveau-svm-refactor-nouveau_range_fault.patch
nouveau-svm-implement-atomic-svm-access.patch


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