github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-05-25 07:33:19 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

mm/khugepaged: fix race with folio split/free using temporary reference

Browse Source 
hpage_collapse_scan_file() calls is_refcount_suitable(), which in turn
calls folio_mapcount().  folio_mapcount() checks folio_test_large() before
proceeding to folio_large_mapcount(), but there is a race window where the
folio may get split/freed between these checks, triggering:

  VM_WARN_ON_FOLIO(!folio_test_large(folio), folio)

Take a temporary reference to the folio in hpage_collapse_scan_file(). 
This stabilizes the folio during refcount check and prevents incorrect
large folio detection due to concurrent split/free.  Use helper
folio_expected_ref_count() + 1 to compare with folio_ref_count() instead
of using is_refcount_suitable().

Link: https://lkml.kernel.org/r/20250526182818.37978-1-shivankg@amd.com
Fixes: 05c5323b2a ("mm: track mapcount of large folios in single value")
Signed-off-by: Shivank Garg <shivankg@amd.com>
Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@google.com
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Fengwei Yin <fengwei.yin@intel.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Shivank Garg 2025-05-26 18:28:18 +00:00 committed by Andrew Morton
parent e13e7922d0
commit 595cf68351
1 changed files with 17 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
mm/khugepaged.c
View File

@ -2293,6 +2293,17 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
continue;
}
if (!folio_try_get(folio)) {
xas_reset(&xas);
continue;
}
if (unlikely(folio != xas_reload(&xas))) {
folio_put(folio);
xas_reset(&xas);
continue;
}
if (folio_order(folio) == HPAGE_PMD_ORDER &&
folio->index == start) {
/* Maybe PMD-mapped */
@ -2303,23 +2314,27 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
* it's safe to skip LRU and refcount checks before
* returning.
*/
folio_put(folio);
break;
}
node = folio_nid(folio);
if (hpage_collapse_scan_abort(node, cc)) {
result = SCAN_SCAN_ABORT;
folio_put(folio);
break;
}
cc->node_load[node]++;
if (!folio_test_lru(folio)) {
result = SCAN_PAGE_LRU;
folio_put(folio);
break;
}
if (!is_refcount_suitable(folio)) {
if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) {
result = SCAN_PAGE_COUNT;
folio_put(folio);
break;
}
@ -2331,6 +2346,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
*/
present += folio_nr_pages(folio);
folio_put(folio);
if (need_resched()) {
xas_pause(&xas);