The patch titled
swapless page migration: fix swapops.h:97 BUG
has been removed from the -mm tree. Its filename is
swapless-page-migration-fix-swapopsh97-bug.patch
This patch was probably dropped from -mm because
it has now been merged into a subsystem tree or
into Linus's tree, or because it was folded into
its parent patch in the -mm tree.
------------------------------------------------------
Subject: swapless page migration: fix swapops.h:97 BUG
From: Hugh Dickins <hugh@xxxxxxxxxxx>
Several times while testing swapless page migration (I've no NUMA, just
hacking it up to migrate recklessly while running load), I've hit the
BUG_ON(!PageLocked(p)) in migration_entry_to_page.
This comes from an orphaned migration entry, unrelated to the current
correctly locked migration, but hit by remove_anon_migration_ptes as it
checks an address in each vma of the anon_vma list.
Such an orphan may be left behind if an earlier migration raced with fork:
copy_one_pte can duplicate a migration entry from parent to child, after
remove_anon_migration_ptes has checked the child vma, but before it has
removed it from the parent vma. (If the process were later to fault on
this orphaned entry, it would hit the same BUG from migration_entry_wait.)
This could be fixed by locking anon_vma in copy_one_pte, but we'd rather
not. There's no such problem with file pages, because vma_prio_tree_add
adds child vma after parent vma, and the page table locking at each end is
enough to serialize. Follow that example with anon_vma: add new vmas to
the tail instead of the head.
(There's no corresponding problem when inserting migration entries, because
a missed pte will leave the page count and mapcount high, which is allowed
for. And there's no corresponding problem when migrating via swap, because
a leftover swap entry will be correctly faulted. But the swapless method
has no refcounting of its entries.)
Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>
Cc: Christoph Lameter <clameter@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
mm/rmap.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff -puN mm/rmap.c~swapless-page-migration-fix-swapopsh97-bug mm/rmap.c
--- 25/mm/rmap.c~swapless-page-migration-fix-swapopsh97-bug Wed May 24 16:11:45 2006
+++ 25-akpm/mm/rmap.c Wed May 24 16:11:45 2006
@@ -103,7 +103,7 @@ int anon_vma_prepare(struct vm_area_stru
spin_lock(&mm->page_table_lock);
if (likely(!vma->anon_vma)) {
vma->anon_vma = anon_vma;
- list_add(&vma->anon_vma_node, &anon_vma->head);
+ list_add_tail(&vma->anon_vma_node, &anon_vma->head);
allocated = NULL;
}
spin_unlock(&mm->page_table_lock);
@@ -127,7 +127,7 @@ void __anon_vma_link(struct vm_area_stru
struct anon_vma *anon_vma = vma->anon_vma;
if (anon_vma) {
- list_add(&vma->anon_vma_node, &anon_vma->head);
+ list_add_tail(&vma->anon_vma_node, &anon_vma->head);
validate_anon_vma(vma);
}
}
@@ -138,7 +138,7 @@ void anon_vma_link(struct vm_area_struct
if (anon_vma) {
spin_lock(&anon_vma->lock);
- list_add(&vma->anon_vma_node, &anon_vma->head);
+ list_add_tail(&vma->anon_vma_node, &anon_vma->head);
validate_anon_vma(vma);
spin_unlock(&anon_vma->lock);
}
_
Patches currently in -mm which might be from hugh@xxxxxxxxxxx are
mm-vm_bug_on.patch
page-migration-make-do_swap_page-redo-the-fault.patch
migration-remove-unnecessary-pageswapcache-checks.patch
swapless-pm-add-r-w-migration-entries.patch
swapless-pm-add-r-w-migration-entries-fix-2.patch
add-page_mkwrite-vm_operations-method.patch
mm-remove-vm_locked-before-remap_pfn_range-and-drop-vm_shm.patch
swapoff-atomic_inc_not_zero-on-mm_users.patch
remove-unused-o_flags-from-do_shmat.patch
page-migration-simplify-migrate_pages.patch
page-migration-simplify-migrate_pages-tweaks.patch
page-migration-handle-freeing-of-pages-in-migrate_pages.patch
page-migration-use-allocator-function-for-migrate_pages.patch
page-migration-support-moving-of-individual-pages.patch
page-migration-detailed-status-for-moving-of-individual-pages.patch
page-migration-support-moving-of-individual-pages-fixes.patch
page-migration-support-a-vma-migration-function.patch
allow-migration-of-mlocked-pages.patch
-
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