exit_mmap() will tear down the VMAs and maple tree with the mmap_lock
held in write mode. Ensure that the maple tree is still valid by
checking ksm_test_exit() after taking the mmap_lock in read mode, but
before the for_each_vma() iterator dereferences a destroyed maple tree.
Since the maple tree is destroyed, the flags telling lockdep to check an
external lock has been cleared. Skip the for_each_vma() iterator to
avoid dereferencing a maple tree without the external lock flag, which
would create a lockdep warning.
Reported-by: Pengfei Xu <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]/
Reported-by: [email protected]
Link: https://syzkaller.appspot.com/bug?id=64a3e95957cd3deab99df7cd7b5a9475af92c93e
Cc: [email protected]
Cc: [email protected]
Cc: Andrew Morton <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: <[email protected]>
Fixes: a5f18ba07276 ("mm/ksm: use vma iterators instead of vma linked list")
Signed-off-by: Liam R. Howlett <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
---
Andrew,
I've included this note because I've changed the subject between v1 and
v2. This is for mm-hotfixes-unstable.
Replaces: b6d4338e8dd2 ("mm/ksm: fix race with ksm_exit() in VMA
iteration")
v1: https://lore.kernel.org/linux-mm/[email protected]/
Changes since v1:
- Commit log & subject.
- Added Acked-by
mm/ksm.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/mm/ksm.c b/mm/ksm.c
index 525c3306e78b..d6280b258ece 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1044,9 +1044,15 @@ static int unmerge_and_remove_all_rmap_items(void)
mm = mm_slot->slot.mm;
mmap_read_lock(mm);
+
+ /*
+ * Exit right away if mm is exiting to avoid lockdep issue in
+ * the maple tree
+ */
+ if (ksm_test_exit(mm))
+ goto mm_exiting;
+
for_each_vma(vmi, vma) {
- if (ksm_test_exit(mm))
- break;
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
continue;
err = unmerge_ksm_pages(vma,
@@ -1055,6 +1061,7 @@ static int unmerge_and_remove_all_rmap_items(void)
goto error;
}
+mm_exiting:
remove_trailing_rmap_items(&mm_slot->rmap_list);
mmap_read_unlock(mm);
--
2.39.2