From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, david@redhat.com, linux-mm@kvack.org,
mhocko@suse.com, mm-commits@vger.kernel.org, osalvador@suse.de,
pasha.tatashin@soleen.com, richard.weiyang@gmail.com,
rientjes@google.com, stable@vger.kernel.org,
torvalds@linux-foundation.org, vbabka@suse.cz
Subject: [patch 11/15] mm/memory_hotplug: drain per-cpu pages again during memory offline
Date: Fri, 18 Sep 2020 21:20:31 -0700 [thread overview]
Message-ID: <20200919042031.EJlTFXy4s%akpm@linux-foundation.org> (raw)
In-Reply-To: <20200918211925.7e97f0ef63d92f5cfe5ccbc5@linux-foundation.org>
From: Pavel Tatashin <pasha.tatashin@soleen.com>
Subject: mm/memory_hotplug: drain per-cpu pages again during memory offline
There is a race during page offline that can lead to infinite loop:
a page never ends up on a buddy list and __offline_pages() keeps
retrying infinitely or until a termination signal is received.
Thread#1 - a new process:
load_elf_binary
begin_new_exec
exec_mmap
mmput
exit_mmap
tlb_finish_mmu
tlb_flush_mmu
release_pages
free_unref_page_list
free_unref_page_prepare
set_pcppage_migratetype(page, migratetype);
// Set page->index migration type below MIGRATE_PCPTYPES
Thread#2 - hot-removes memory
__offline_pages
start_isolate_page_range
set_migratetype_isolate
set_pageblock_migratetype(page, MIGRATE_ISOLATE);
Set migration type to MIGRATE_ISOLATE-> set
drain_all_pages(zone);
// drain per-cpu page lists to buddy allocator.
Thread#1 - continue
free_unref_page_commit
migratetype = get_pcppage_migratetype(page);
// get old migration type
list_add(&page->lru, &pcp->lists[migratetype]);
// add new page to already drained pcp list
Thread#2
Never drains pcp again, and therefore gets stuck in the loop.
The fix is to try to drain per-cpu lists again after
check_pages_isolated_cb() fails.
Link: https://lkml.kernel.org/r/20200903140032.380431-1-pasha.tatashin@soleen.com
Link: https://lkml.kernel.org/r/20200904151448.100489-2-pasha.tatashin@soleen.com
Link: http://lkml.kernel.org/r/20200904070235.GA15277@dhcp22.suse.cz
Fixes: c52e75935f8d ("mm: remove extra drain pages on pcp list")
Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/memory_hotplug.c | 14 ++++++++++++++
mm/page_isolation.c | 8 ++++++++
2 files changed, 22 insertions(+)
--- a/mm/memory_hotplug.c~mm-memory_hotplug-drain-per-cpu-pages-again-during-memory-offline
+++ a/mm/memory_hotplug.c
@@ -1575,6 +1575,20 @@ static int __ref __offline_pages(unsigne
/* check again */
ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
NULL, check_pages_isolated_cb);
+ /*
+ * per-cpu pages are drained in start_isolate_page_range, but if
+ * there are still pages that are not free, make sure that we
+ * drain again, because when we isolated range we might
+ * have raced with another thread that was adding pages to pcp
+ * list.
+ *
+ * Forward progress should be still guaranteed because
+ * pages on the pcp list can only belong to MOVABLE_ZONE
+ * because has_unmovable_pages explicitly checks for
+ * PageBuddy on freed pages on other zones.
+ */
+ if (ret)
+ drain_all_pages(zone);
} while (ret);
/* Ok, all of our target is isolated.
--- a/mm/page_isolation.c~mm-memory_hotplug-drain-per-cpu-pages-again-during-memory-offline
+++ a/mm/page_isolation.c
@@ -170,6 +170,14 @@ __first_valid_page(unsigned long pfn, un
* pageblocks we may have modified and return -EBUSY to caller. This
* prevents two threads from simultaneously working on overlapping ranges.
*
+ * Please note that there is no strong synchronization with the page allocator
+ * either. Pages might be freed while their page blocks are marked ISOLATED.
+ * In some cases pages might still end up on pcp lists and that would allow
+ * for their allocation even when they are in fact isolated already. Depending
+ * on how strong of a guarantee the caller needs drain_all_pages might be needed
+ * (e.g. __offline_pages will need to call it after check for isolated range for
+ * a next retry).
+ *
* Return: the number of isolated pageblocks on success and -EBUSY if any part
* of range cannot be isolated.
*/
_
next prev parent reply other threads:[~2020-09-19 4:20 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-19 4:19 incoming Andrew Morton
2020-09-19 4:20 ` [patch 01/15] mailmap: add older email addresses for Kees Cook Andrew Morton
2020-09-19 4:20 ` [patch 02/15] ksm: reinstate memcg charge on copied pages Andrew Morton
2020-09-19 4:20 ` [patch 03/15] mm: migration of hugetlbfs page skip memcg Andrew Morton
2020-09-19 4:20 ` [patch 04/15] shmem: shmem_writepage() split unlikely i915 THP Andrew Morton
2020-09-19 4:20 ` [patch 05/15] mm: fix check_move_unevictable_pages() on THP Andrew Morton
2020-09-19 4:20 ` [patch 06/15] mlock: fix unevictable_pgs event counts " Andrew Morton
2020-09-19 4:20 ` [patch 07/15] tmpfs: restore functionality of nr_inodes=0 Andrew Morton
2020-09-19 4:20 ` [patch 08/15] kprobes: fix kill kprobe which has been marked as gone Andrew Morton
2020-09-19 4:20 ` [patch 09/15] mm/thp: fix __split_huge_pmd_locked() for migration PMD Andrew Morton
2020-09-19 4:20 ` [patch 10/15] selftests/vm: fix display of page size in map_hugetlb Andrew Morton
2020-09-19 4:20 ` Andrew Morton [this message]
2020-09-19 4:20 ` [patch 12/15] ftrace: let ftrace_enable_sysctl take a kernel pointer buffer Andrew Morton
2020-09-19 4:20 ` [patch 13/15] stackleak: let stack_erasing_sysctl " Andrew Morton
2020-09-19 4:20 ` [patch 14/15] fs/fs-writeback.c: adjust dirtytime_interval_handler definition to match prototype Andrew Morton
2020-09-19 4:20 ` [patch 15/15] kcsan: kconfig: move to menu 'Generic Kernel Debugging Instruments' Andrew Morton
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