The patch titled
Subject: mm/ksm: fix race with VMA iteration and mm_struct teardown
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-ksm-fix-race-with-vma-iteration-and-mm_struct-teardown.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patche…
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: "Liam R. Howlett" <Liam.Howlett(a)oracle.com>
Subject: mm/ksm: fix race with VMA iteration and mm_struct teardown
Date: Wed, 8 Mar 2023 17:03:10 -0500
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@oracle.com
Fixes: a5f18ba07276 ("mm/ksm: use vma iterators instead of vma linked list")
Signed-off-by: Liam R. Howlett <Liam.Howlett(a)oracle.com>
Reported-by: Pengfei Xu <pengfei.xu(a)intel.com>
Link: https://lore.kernel.org/lkml/ZAdUUhSbaa6fHS36@xpf.sh.intel.com/
Reported-by: syzbot+2ee18845e89ae76342c5(a)syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=64a3e95957cd3deab99df7cd7b5a9475af92c9…
Acked-by: David Hildenbrand <david(a)redhat.com>
Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org>
Cc: <heng.su(a)intel.com>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
--- a/mm/ksm.c~mm-ksm-fix-race-with-vma-iteration-and-mm_struct-teardown
+++ a/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 -mm which might be from Liam.Howlett(a)oracle.com are
maple_tree-fix-mas_skip_node-end-slot-detection.patch
test_maple_tree-add-more-testing-for-mas_empty_area.patch
mm-ksm-fix-race-with-vma-iteration-and-mm_struct-teardown.patch
maple_tree-be-more-cautious-about-dead-nodes.patch
maple_tree-detect-dead-nodes-in-mas_start.patch
maple_tree-fix-freeing-of-nodes-in-rcu-mode.patch
maple_tree-remove-extra-smp_wmb-from-mas_dead_leaves.patch
maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode.patch
maple_tree-add-smp_rmb-to-dead-node-detection.patch
maple_tree-add-rcu-lock-checking-to-rcu-callback-functions.patch
mm-enable-maple-tree-rcu-mode-by-default.patch
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 <pengfei.xu(a)intel.com>
Link: https://lore.kernel.org/lkml/ZAdUUhSbaa6fHS36@xpf.sh.intel.com/
Reported-by: syzbot+2ee18845e89ae76342c5(a)syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=64a3e95957cd3deab99df7cd7b5a9475af92c9…
Cc: linux-mm(a)kvack.org
Cc: linux-kernel(a)vger.kernel.org
Cc: Andrew Morton <akpm(a)linux-foundation.org>
Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org>
Cc: heng.su(a)intel.com
Cc: lkp(a)intel.com
Cc: <Stable(a)vger.kernel.org>
Fixes: a5f18ba07276 ("mm/ksm: use vma iterators instead of vma linked list")
Signed-off-by: Liam R. Howlett <Liam.Howlett(a)oracle.com>
Acked-by: David Hildenbrand <david(a)redhat.com>
---
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/20230307205951.2465275-1-Liam.Howlett@orac…
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