[PATCH 3.2 098/125] mm: revert 0def08e3 ("mm/mempolicy.c: check return code of check_range")

Ben Hutchings
2014-07-08T19:28:30Z

From: Minchan Kim <minchan@kernel.org>

commit 082708072a4250f5c4dbc62065e7af93f5e45646 upstream.

Revert commit 0def08e3acc2 because check_range can't fail in
migrate_to_node with considering current usecases.

Quote from Johannes

: I think it makes sense to revert. Not because of the semantics, but I
: just don't see how check_range() could even fail for this callsite:
:
: 1. we pass mm->mmap->vm_start in there, so we should not fail due to
: find_vma()
:
: 2. we pass MPOL_MF_DISCONTIG_OK, so the discontig checks do not apply
: and so can not fail
:
: 3. we pass MPOL_MF_MOVE | MPOL_MF_MOVE_ALL, the page table loops will
: continue until addr == end, so we never fail with -EIO

And I added a new VM_BUG_ON for checking migrate_to_node's future usecase
which might pass to MPOL_MF_STRICT.

Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vasiliy Kulikov <segooon@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
mm/mempolicy.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -945,15 +945,18 @@ static int migrate_to_node(struct mm_str
nodemask_t nmask;
LIST_HEAD(pagelist);
int err = 0;
- struct vm_area_struct *vma;

nodes_clear(nmask);
node_set(source, nmask);

- vma = check_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
+ /*
+ * This does not "check" the range but isolates all pages that
+ * need migration. Between passing in the full user address
+ * space range and MPOL_MF_DISCONTIG_OK, this call can not fail.
+ */
+ VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
+ check_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
flags | MPOL_MF_DISCONTIG_OK, &pagelist);
- if (IS_ERR(vma))
- return PTR_ERR(vma);

if (!list_empty(&pagelist)) {
err = migrate_pages(&pagelist, new_node_page, dest,