6.5-stable review patch. If anyone has any objections, please let me know.
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From: Johannes Weiner hannes@cmpxchg.org
commit 7b086755fb8cdbb6b3e45a1bbddc00e7f9b1dc03 upstream.
Commit 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock") bypasses the pcplist on lock contention and returns the page directly to the buddy list of the page's migratetype.
For pages that don't have their own pcplist, such as CMA and HIGHATOMIC, the migratetype is temporarily updated such that the page can hitch a ride on the MOVABLE pcplist. Their true type is later reassessed when flushing in free_pcppages_bulk(). However, when lock contention is detected after the type was already overridden, the bypass will then put the page on the wrong buddy list.
Once on the MOVABLE buddy list, the page becomes eligible for fallbacks and even stealing. In the case of HIGHATOMIC, otherwise ineligible allocations can dip into the highatomic reserves. In the case of CMA, the page can be lost from the CMA region permanently.
Use a separate pcpmigratetype variable for the pcplist override. Use the original migratetype when going directly to the buddy. This fixes the bug and should make the intentions more obvious in the code.
Originally sent here to address the HIGHATOMIC case: https://lore.kernel.org/lkml/20230821183733.106619-4-hannes@cmpxchg.org/
Changelog updated in response to the CMA-specific bug report.
[mgorman@techsingularity.net: updated changelog] Link: https://lkml.kernel.org/r/20230911181108.GA104295@cmpxchg.org Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock") Signed-off-by: Johannes Weiner hannes@cmpxchg.org Reported-by: Joe Liu joe.liu@mediatek.com Reviewed-by: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/page_alloc.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
--- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2438,7 +2438,7 @@ void free_unref_page(struct page *page, struct per_cpu_pages *pcp; struct zone *zone; unsigned long pfn = page_to_pfn(page); - int migratetype; + int migratetype, pcpmigratetype;
if (!free_unref_page_prepare(page, pfn, order)) return; @@ -2446,24 +2446,24 @@ void free_unref_page(struct page *page, /* * We only track unmovable, reclaimable and movable on pcp lists. * Place ISOLATE pages on the isolated list because they are being - * offlined but treat HIGHATOMIC as movable pages so we can get those - * areas back if necessary. Otherwise, we may have to free + * offlined but treat HIGHATOMIC and CMA as movable pages so we can + * get those areas back if necessary. Otherwise, we may have to free * excessively into the page allocator */ - migratetype = get_pcppage_migratetype(page); + migratetype = pcpmigratetype = get_pcppage_migratetype(page); if (unlikely(migratetype >= MIGRATE_PCPTYPES)) { if (unlikely(is_migrate_isolate(migratetype))) { free_one_page(page_zone(page), page, pfn, order, migratetype, FPI_NONE); return; } - migratetype = MIGRATE_MOVABLE; + pcpmigratetype = MIGRATE_MOVABLE; }
zone = page_zone(page); pcp_trylock_prepare(UP_flags); pcp = pcp_spin_trylock(zone->per_cpu_pageset); if (pcp) { - free_unref_page_commit(zone, pcp, page, migratetype, order); + free_unref_page_commit(zone, pcp, page, pcpmigratetype, order); pcp_spin_unlock(pcp); } else { free_one_page(zone, page, pfn, order, migratetype, FPI_NONE);