99 lines
3.0 KiB
Diff
99 lines
3.0 KiB
Diff
From c041325f222c774573ad73d35939451a4e221e52 Mon Sep 17 00:00:00 2001
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From: Shivank Garg <shivankg@amd.com>
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Date: Mon, 26 May 2025 18:28:18 +0000
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Subject: mm/khugepaged: fix race with folio split/free using temporary
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reference
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hpage_collapse_scan_file() calls is_refcount_suitable(), which in turn
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calls folio_mapcount(). folio_mapcount() checks folio_test_large() before
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proceeding to folio_large_mapcount(), but there is a race window where the
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folio may get split/freed between these checks, triggering:
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VM_WARN_ON_FOLIO(!folio_test_large(folio), folio)
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Take a temporary reference to the folio in hpage_collapse_scan_file().
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This stabilizes the folio during refcount check and prevents incorrect
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large folio detection due to concurrent split/free. Use helper
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folio_expected_ref_count() + 1 to compare with folio_ref_count() instead
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of using is_refcount_suitable().
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Link: https://lkml.kernel.org/r/20250526182818.37978-1-shivankg@amd.com
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Fixes: 05c5323b2a34 ("mm: track mapcount of large folios in single value")
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Signed-off-by: Shivank Garg <shivankg@amd.com>
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Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com
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Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@google.com
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Suggested-by: David Hildenbrand <david@redhat.com>
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Acked-by: David Hildenbrand <david@redhat.com>
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Acked-by: Dev Jain <dev.jain@arm.com>
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Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
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Cc: Bharata B Rao <bharata@amd.com>
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Cc: Fengwei Yin <fengwei.yin@intel.com>
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Cc: Liam Howlett <liam.howlett@oracle.com>
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Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
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Cc: Mariano Pache <npache@redhat.com>
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Cc: Ryan Roberts <ryan.roberts@arm.com>
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Cc: Zi Yan <ziy@nvidia.com>
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Cc: <stable@vger.kernel.org>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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---
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mm/khugepaged.c | 18 +++++++++++++++++-
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1 file changed, 17 insertions(+), 1 deletion(-)
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--- a/mm/khugepaged.c
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+++ b/mm/khugepaged.c
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@@ -2295,6 +2295,17 @@ static int hpage_collapse_scan_file(stru
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continue;
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}
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+ if (!folio_try_get(folio)) {
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+ xas_reset(&xas);
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+ continue;
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+ }
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+
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+ if (unlikely(folio != xas_reload(&xas))) {
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+ folio_put(folio);
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+ xas_reset(&xas);
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+ continue;
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+ }
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+
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if (folio_order(folio) == HPAGE_PMD_ORDER &&
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folio->index == start) {
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/* Maybe PMD-mapped */
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@@ -2305,23 +2316,27 @@ static int hpage_collapse_scan_file(stru
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* it's safe to skip LRU and refcount checks before
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* returning.
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*/
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+ folio_put(folio);
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break;
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}
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node = folio_nid(folio);
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if (hpage_collapse_scan_abort(node, cc)) {
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result = SCAN_SCAN_ABORT;
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+ folio_put(folio);
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break;
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}
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cc->node_load[node]++;
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if (!folio_test_lru(folio)) {
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result = SCAN_PAGE_LRU;
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+ folio_put(folio);
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break;
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}
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- if (!is_refcount_suitable(folio)) {
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+ if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) {
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result = SCAN_PAGE_COUNT;
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+ folio_put(folio);
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break;
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}
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@@ -2333,6 +2348,7 @@ static int hpage_collapse_scan_file(stru
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*/
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present += folio_nr_pages(folio);
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+ folio_put(folio);
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if (need_resched()) {
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xas_pause(&xas);
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