The patch titled
Date: Fri, 5 Jan 2024 16:57:29 +0100
has been added to the -mm mm-nonmm-unstable branch. Its filename is
mm-rmap-silence-vm_warn_on_folio-in-__folio_rmap_sanity_checks.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-rmap-silence-vm_warn_on_folio-in-__folio_rmap_sanity_checks.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Date: Fri, 5 Jan 2024 16:57:29 +0100
Subject: mm/rmap: silence VM_WARN_ON_FOLIO() in __folio_rmap_sanity_checks()
Unfortunately, vm_insert_page() and friends and up passing
driver-allocated folios into folio_add_file_rmap_pte() using
insert_page_into_pte_locked().
While these driver-allocated folios can be compound pages (large folios),
they are not proper "rmappable" folios.
In these VM_MIXEDMAP VMAs, there isn't really the concept of a reverse
mapping, so long-term, we should clean that up and not call into rmap
code.
For the time being, document how we can end up in rmap code with large
folios that are not marked rmappable.
Link: https://lkml.kernel.org/r/793c5cee-d5fc-4eb1-86a2-39e05686233d@xxxxxxxxxx
Fixes: 68f0320824fa ("mm/rmap: convert folio_add_file_rmap_range() into folio_add_file_rmap_[pte|ptes|pmd]()")
Reported-by: syzbot+50ef73537bbc393a25bb@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lkml.kernel.org/r/000000000000014174060e09316e@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/rmap.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- a/include/linux/rmap.h~mm-rmap-silence-vm_warn_on_folio-in-__folio_rmap_sanity_checks
+++ a/include/linux/rmap.h
@@ -199,8 +199,15 @@ static inline void __folio_rmap_sanity_c
{
/* hugetlb folios are handled separately. */
VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
- VM_WARN_ON_FOLIO(folio_test_large(folio) &&
- !folio_test_large_rmappable(folio), folio);
+
+ /*
+ * TODO: we get driver-allocated folios that have nothing to do with
+ * the rmap using vm_insert_page(); therefore, we cannot assume that
+ * folio_test_large_rmappable() holds for large folios. We should
+ * handle any desired mapcount+stats accounting for these folios in
+ * VM_MIXEDMAP VMAs separately, and then sanity-check here that
+ * we really only get rmappable folios.
+ */
VM_WARN_ON_ONCE(nr_pages <= 0);
VM_WARN_ON_FOLIO(page_folio(page) != folio, folio);
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-rmap-silence-vm_warn_on_folio-in-__folio_rmap_sanity_checks.patch
