mm: fix a potential infinite loop in start_isolate_page_range()

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=0x10000, split_pfn_offset=0xc000,
free_page_order should first be 0x8000 then 0x4000, instead of 0x4000 then
0x8000, which the original algorithm did.

[akpm@linux-foundation.org: suppress min() warning]
Link: https://lkml.kernel.org/r/20220524194756.1698351-1-zi.yan@sent.com
Fixes: b2c9e2fbba3253 ("mm: make alloc_contig_range work at pageblock granularity")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reported-by: Qian Cai <quic_qiancai@quicinc.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Hildenbrand <david@redhat.com>
Cc: Eric Ren <renzhengeek@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 267599dd970631e71b791d8f4d760fb15150cfbe..bc93a82e51e6027dd9f30ea83161a8cdb37675c0 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1114,13 +1114,18 @@ void split_free_page(struct page *free_page,
        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_t(int,
+                                       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;

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index b3f074d1682ef07db30fec559e5fc43289b9ec9e..c643c8420809bd49383a59074d0cb671c976b630 100644 (file)
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -283,6 +283,7 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  * 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, unsigned long nr_pages)
  * 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(unsigned long boundary_pfn, gfp_t gfp_flags,
                                      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(unsigned long boundary_pfn, gfp_t gfp_flags,
                        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(unsigned long boundary_pfn, gfp_t gfp_flags,
                        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(unsigned long boundary_pfn, gfp_t gfp_flags,
                                };
                                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(unsigned long boundary_pfn, gfp_t gfp_flags,
                                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(unsigned long boundary_pfn, gfp_t gfp_flags,
        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 long start_pfn, unsigned long end_pfn,
        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;