The patch titled
Subject: mm: fix a potential infinite loop in start_isolate_page_range()
has been added to the -mm mm-unstable branch. Its filename is
mm-fix-a-potential-infinite-loop-in-start_isolate_page_range.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-a-potential-infinite-loop-in-start_isolate_page_range.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Zi Yan <ziy@xxxxxxxxxx>
Subject: mm: fix a potential infinite loop in start_isolate_page_range()
Date: Tue, 24 May 2022 15:47:56 -0400
In isolate_single_pageblock() called by start_isolate_page_range(), there
are some pageblock isolation issues causing a potential infinite loop when
isolating a page range. This is reported by Qian Cai.
1. the pageblock was isolated by just changing pageblock migratetype
without checking unmovable pages. Calling set_migratetype_isolate() to
isolate pageblock properly.
2. an off-by-one error caused migrating pages unnecessarily, since the page
is not crossing pageblock boundary.
3. migrating a compound page across pageblock boundary then splitting the
free page later has a small race window that the free page might be
allocated again, so that the code will try again, causing an potential
infinite loop. Temporarily set the to-be-migrated page's pageblock to
MIGRATE_ISOLATE to prevent that and bail out early if no free page is
found after page migration.
An additional fix to split_free_page() aims to avoid crashing in
__free_one_page(). When the free page is split at the specified
split_pfn_offset, free_page_order should check both the first bit of
free_page_pfn and the last bit of split_pfn_offset and use the smaller
one. For example, if free_page_pfn=3D0x10000, split_pfn_offset=3D0xc000,
free_page_order should first be 0x8000 then 0x4000, instead of 0x4000 then
0x8000, which the original algorithm did.
Link: https://lkml.kernel.org/r/20220524194756.1698351-1-zi.yan@xxxxxxxx
Fixes: b2c9e2fbba ("mm: make alloc_contig_range work at pageblock granulari=
ty")
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Reported-by: Qian Cai <quic_qiancai@xxxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Eric Ren <renzhengeek@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 5 +++-
mm/page_isolation.c | 52 ++++++++++++++++++++++++++++++++----------
2 files changed, 44 insertions(+), 13 deletions(-)
--- a/mm/page_alloc.c~mm-fix-a-potential-infinite-loop-in-start_isolate_page_range
+++ a/mm/page_alloc.c
@@ -1114,13 +1114,16 @@ void split_free_page(struct page *free_p
unsigned long flags;
int free_page_order;
+ if (split_pfn_offset == 0)
+ return;
+
spin_lock_irqsave(&zone->lock, flags);
del_page_from_free_list(free_page, zone, order);
for (pfn = free_page_pfn;
pfn < free_page_pfn + (1UL << order);) {
int mt = get_pfnblock_migratetype(pfn_to_page(pfn), pfn);
- free_page_order = ffs(split_pfn_offset) - 1;
+ free_page_order = min(pfn ? __ffs(pfn) : order, __fls(split_pfn_offset));
__free_one_page(pfn_to_page(pfn), pfn, zone, free_page_order,
mt, FPI_NONE);
pfn += 1UL << free_page_order;
--- a/mm/page_isolation.c~mm-fix-a-potential-infinite-loop-in-start_isolate_page_range
+++ a/mm/page_isolation.c
@@ -283,6 +283,7 @@ __first_valid_page(unsigned long pfn, un
* isolate_single_pageblock() -- tries to isolate a pageblock that might be
* within a free or in-use page.
* @boundary_pfn: pageblock-aligned pfn that a page might cross
+ * @flags: isolation flags
* @gfp_flags: GFP flags used for migrating pages
* @isolate_before: isolate the pageblock before the boundary_pfn
*
@@ -298,14 +299,15 @@ __first_valid_page(unsigned long pfn, un
* either. The function handles this by splitting the free page or migrating
* the in-use page then splitting the free page.
*/
-static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
- bool isolate_before)
+static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
+ gfp_t gfp_flags, bool isolate_before)
{
unsigned char saved_mt;
unsigned long start_pfn;
unsigned long isolate_pageblock;
unsigned long pfn;
struct zone *zone;
+ int ret;
VM_BUG_ON(!IS_ALIGNED(boundary_pfn, pageblock_nr_pages));
@@ -325,7 +327,11 @@ static int isolate_single_pageblock(unsi
zone->zone_start_pfn);
saved_mt = get_pageblock_migratetype(pfn_to_page(isolate_pageblock));
- set_pageblock_migratetype(pfn_to_page(isolate_pageblock), MIGRATE_ISOLATE);
+ ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt, flags,
+ isolate_pageblock, isolate_pageblock + pageblock_nr_pages);
+
+ if (ret)
+ return ret;
/*
* Bail out early when the to-be-isolated pageblock does not form
@@ -374,7 +380,7 @@ static int isolate_single_pageblock(unsi
struct page *head = compound_head(page);
unsigned long head_pfn = page_to_pfn(head);
- if (head_pfn + nr_pages < boundary_pfn) {
+ if (head_pfn + nr_pages <= boundary_pfn) {
pfn = head_pfn + nr_pages;
continue;
}
@@ -386,7 +392,8 @@ static int isolate_single_pageblock(unsi
if (PageHuge(page) || PageLRU(page) || __PageMovable(page)) {
int order;
unsigned long outer_pfn;
- int ret;
+ int page_mt = get_pageblock_migratetype(page);
+ bool isolate_page = !is_migrate_isolate_page(page);
struct compact_control cc = {
.nr_migratepages = 0,
.order = -1,
@@ -399,9 +406,31 @@ static int isolate_single_pageblock(unsi
};
INIT_LIST_HEAD(&cc.migratepages);
+ /*
+ * XXX: mark the page as MIGRATE_ISOLATE so that
+ * no one else can grab the freed page after migration.
+ * Ideally, the page should be freed as two separate
+ * pages to be added into separate migratetype free
+ * lists.
+ */
+ if (isolate_page) {
+ ret = set_migratetype_isolate(page, page_mt,
+ flags, head_pfn, head_pfn + nr_pages);
+ if (ret)
+ goto failed;
+ }
+
ret = __alloc_contig_migrate_range(&cc, head_pfn,
head_pfn + nr_pages);
+ /*
+ * restore the page's migratetype so that it can
+ * be split into separate migratetype free lists
+ * later.
+ */
+ if (isolate_page)
+ unset_migratetype_isolate(page, page_mt);
+
if (ret)
goto failed;
/*
@@ -417,10 +446,9 @@ static int isolate_single_pageblock(unsi
order = 0;
outer_pfn = pfn;
while (!PageBuddy(pfn_to_page(outer_pfn))) {
- if (++order >= MAX_ORDER) {
- outer_pfn = pfn;
- break;
- }
+ /* stop if we cannot find the free page */
+ if (++order >= MAX_ORDER)
+ goto failed;
outer_pfn &= ~0UL << order;
}
pfn = outer_pfn;
@@ -435,7 +463,7 @@ static int isolate_single_pageblock(unsi
return 0;
failed:
/* restore the original migratetype */
- set_pageblock_migratetype(pfn_to_page(isolate_pageblock), saved_mt);
+ unset_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt);
return -EBUSY;
}
@@ -496,12 +524,12 @@ int start_isolate_page_range(unsigned lo
int ret;
/* isolate [isolate_start, isolate_start + pageblock_nr_pages) pageblock */
- ret = isolate_single_pageblock(isolate_start, gfp_flags, false);
+ ret = isolate_single_pageblock(isolate_start, flags, gfp_flags, false);
if (ret)
return ret;
/* isolate [isolate_end - pageblock_nr_pages, isolate_end) pageblock */
- ret = isolate_single_pageblock(isolate_end, gfp_flags, true);
+ ret = isolate_single_pageblock(isolate_end, flags, gfp_flags, true);
if (ret) {
unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype);
return ret;
_
Patches currently in -mm which might be from ziy@xxxxxxxxxx are
mm-fix-a-potential-infinite-loop-in-start_isolate_page_range.patch
