On Thu 03-09-20 12:29:01, Andrew Morton wrote:
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 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 Cc: Michal Hocko mhocko@suse.com Cc: Oscar Salvador osalvador@suse.de Cc: Wei Yang richard.weiyang@gmail.com Cc: David Hildenbrand david@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org
Acked-by: Michal Hocko mhocko@suse.com
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);/* 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.
_
Patches currently in -mm which might be from pasha.tatashin@soleen.com are
mm-memory_hotplug-drain-per-cpu-pages-again-during-memory-offline.patch