This is a note to let you know that I've just added the patch titled
mm/ksm: fix race with VMA iteration and mm_struct teardown
to the 6.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-ksm-fix-race-with-vma-iteration-and-mm_struct-teardown.patch
and it can be found in the queue-6.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 6db504ce55bdbc575723938fc480713c9183f6a2 Mon Sep 17 00:00:00 2001
From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
Date: Wed, 8 Mar 2023 17:03:10 -0500
Subject: mm/ksm: fix race with VMA iteration and mm_struct teardown
From: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
commit 6db504ce55bdbc575723938fc480713c9183f6a2 upstream.
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.
Link: https://lkml.kernel.org/r/20230308220310.3119196-1-Liam.Howlett@xxxxxxxxxx
Fixes: a5f18ba07276 ("mm/ksm: use vma iterators instead of vma linked list")
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Reported-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Link: https://lore.kernel.org/lkml/ZAdUUhSbaa6fHS36@xxxxxxxxxxxxxxxx/
Reported-by: syzbot+2ee18845e89ae76342c5@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://syzkaller.appspot.com/bug?id=64a3e95957cd3deab99df7cd7b5a9475af92c93e
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: <heng.su@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/ksm.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -988,9 +988,15 @@ static int unmerge_and_remove_all_rmap_i
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,
@@ -999,6 +1005,7 @@ static int unmerge_and_remove_all_rmap_i
goto error;
}
+mm_exiting:
remove_trailing_rmap_items(&mm_slot->rmap_list);
mmap_read_unlock(mm);
Patches currently in stable-queue which might be from Liam.Howlett@xxxxxxxxxx are
queue-6.2/mm-ksm-fix-race-with-vma-iteration-and-mm_struct-teardown.patch
queue-6.2/maple_tree-fix-mas_skip_node-end-slot-detection.patch
queue-6.2/test_maple_tree-add-more-testing-for-mas_empty_area.patch
