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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.
Fixes: c52e75935f
("mm: remove extra drain pages on pcp list")
Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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>
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
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
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2 changed files with 22 additions and 0 deletions
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@ -1575,6 +1575,20 @@ static int __ref __offline_pages(unsigned long start_pfn,
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/* check again */
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ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
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NULL, check_pages_isolated_cb);
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/*
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* per-cpu pages are drained in start_isolate_page_range, but if
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* there are still pages that are not free, make sure that we
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* drain again, because when we isolated range we might
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* have raced with another thread that was adding pages to pcp
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* list.
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*
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* Forward progress should be still guaranteed because
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* pages on the pcp list can only belong to MOVABLE_ZONE
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* because has_unmovable_pages explicitly checks for
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* PageBuddy on freed pages on other zones.
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*/
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if (ret)
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drain_all_pages(zone);
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} while (ret);
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/* Ok, all of our target is isolated.
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@ -170,6 +170,14 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
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* pageblocks we may have modified and return -EBUSY to caller. This
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* prevents two threads from simultaneously working on overlapping ranges.
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*
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* Please note that there is no strong synchronization with the page allocator
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* either. Pages might be freed while their page blocks are marked ISOLATED.
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* In some cases pages might still end up on pcp lists and that would allow
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* for their allocation even when they are in fact isolated already. Depending
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* on how strong of a guarantee the caller needs drain_all_pages might be needed
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* (e.g. __offline_pages will need to call it after check for isolated range for
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* a next retry).
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*
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* Return: the number of isolated pageblocks on success and -EBUSY if any part
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* of range cannot be isolated.
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*/
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