The patch titled
Subject: mempolicy: migration attempt to match interleave nodes: fix
has been added to the -mm mm-unstable branch. Its filename is
mempolicy-migration-attempt-to-match-interleave-nodes-fix.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mempolicy-migration-attempt-to-match-interleave-nodes-fix.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mempolicy: migration attempt to match interleave nodes: fix
Date: Mon, 23 Oct 2023 23:50:42 -0700 (PDT)
mm-unstable commit edd33b8807a1 ("mempolicy: migration attempt to match
interleave nodes") added a second vma_iter search to do_mbind(), to
determine the interleave index to be used in the MPOL_INTERLEAVE case.
But sadly it added it just after the mmap_write_unlock(), leaving this new
VMA search unprotected: and so syzbot reports suspicious RCU usage from
lib/maple_tree.c:856.
This could be fixed with an rcu_read_lock/unlock() pair (per Liam); but
since we have been relying on the mmap_lock up to this point, it's
slightly better to extend it over the new search too, for a well-defined
result consistent with the policy this mbind() is establishing (rather
than whatever might follow once the mmap_lock is dropped).
Link: https://lkml.kernel.org/r/3311d544-fb05-a7f1-1b74-16aa0f6cd4fe@xxxxxxxxxx
Fixes: edd33b8807a1 ("mempolicy: migration attempt to match interleave nodes")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reported-by: syzbot+79fcba037b6df73756d3@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/linux-mm/000000000000c05f1b0608657fde@xxxxxxxxxx/
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mempolicy.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/mm/mempolicy.c~mempolicy-migration-attempt-to-match-interleave-nodes-fix
+++ a/mm/mempolicy.c
@@ -1293,8 +1293,6 @@ static long do_mbind(unsigned long start
}
}
- mmap_write_unlock(mm);
-
if (!err && !list_empty(&pagelist)) {
/* Convert MPOL_DEFAULT's NULL to task or default policy */
if (!new) {
@@ -1336,7 +1334,11 @@ static long do_mbind(unsigned long start
mmpol.ilx -= page->index >> order;
}
}
+ }
+ mmap_write_unlock(mm);
+
+ if (!err && !list_empty(&pagelist)) {
nr_failed |= migrate_pages(&pagelist,
alloc_migration_target_by_mpol, NULL,
(unsigned long)&mmpol, MIGRATE_SYNC,
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
hugetlbfs-drop-shared-numa-mempolicy-pretence.patch
kernfs-drop-shared-numa-mempolicy-hooks.patch
mempolicy-fix-migrate_pages2-syscall-return-nr_failed.patch
mempolicy-trivia-delete-those-ancient-pr_debugs.patch
mempolicy-trivia-slightly-more-consistent-naming.patch
mempolicy-trivia-use-pgoff_t-in-shared-mempolicy-tree.patch
mempolicy-mpol_shared_policy_init-without-pseudo-vma.patch
mempolicy-remove-confusing-mpol_mf_lazy-dead-code.patch
mm-add-page_rmappable_folio-wrapper.patch
mempolicy-alloc_pages_mpol-for-numa-policy-without-vma.patch
mempolicy-mmap_lock-is-not-needed-while-migrating-folios.patch
mempolicy-migration-attempt-to-match-interleave-nodes.patch
mempolicy-migration-attempt-to-match-interleave-nodes-fix.patch
ext4-add-__gfp_nowarn-to-gfp_nowait-in-readahead.patch
mm-mlock-avoid-folio_within_range-on-ksm-pages.patch
