This is a note to let you know that I've just added the patch titled
mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS
to the 4.9-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-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 5b53a6ea886700a128b697a6fe8375340dea2c30 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@xxxxxxxx>
Date: Fri, 18 Aug 2017 15:16:12 -0700
Subject: mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS
From: Michal Hocko <mhocko@xxxxxxxx>
commit 5b53a6ea886700a128b697a6fe8375340dea2c30 upstream.
Tetsuo Handa has noticed that MMF_UNSTABLE SIGBUS path in
handle_mm_fault causes a lockdep splat
Out of memory: Kill process 1056 (a.out) score 603 or sacrifice child
Killed process 1056 (a.out) total-vm:4268108kB, anon-rss:2246048kB, file-rss:0kB, shmem-rss:0kB
a.out (1169) used greatest stack depth: 11664 bytes left
DEBUG_LOCKS_WARN_ON(depth <= 0)
------------[ cut here ]------------
WARNING: CPU: 6 PID: 1339 at kernel/locking/lockdep.c:3617 lock_release+0x172/0x1e0
CPU: 6 PID: 1339 Comm: a.out Not tainted 4.13.0-rc3-next-20170803+ #142
Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
RIP: 0010:lock_release+0x172/0x1e0
Call Trace:
up_read+0x1a/0x40
__do_page_fault+0x28e/0x4c0
do_page_fault+0x30/0x80
page_fault+0x28/0x30
The reason is that the page fault path might have dropped the mmap_sem
and returned with VM_FAULT_RETRY. MMF_UNSTABLE check however rewrites
the error path to VM_FAULT_SIGBUS and we always expect mmap_sem taken in
that path. Fix this by taking mmap_sem when VM_FAULT_RETRY is held in
the MMF_UNSTABLE path.
We cannot simply add VM_FAULT_SIGBUS to the existing error code because
all arch specific page fault handlers and g-u-p would have to learn a
new error code combination.
Link: http://lkml.kernel.org/r/20170807113839.16695-2-mhocko@xxxxxxxxxx
Fixes: 3f70dc38cec2 ("mm: make sure that kthreads will not refault oom reaped memory")
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Andrea Argangeli <andrea@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Wenwei Tao <wenwei.tww@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3635,8 +3635,18 @@ int handle_mm_fault(struct vm_area_struc
* further.
*/
if (unlikely((current->flags & PF_KTHREAD) && !(ret & VM_FAULT_ERROR)
- && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags)))
+ && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags))) {
+
+ /*
+ * We are going to enforce SIGBUS but the PF path might have
+ * dropped the mmap_sem already so take it again so that
+ * we do not break expectations of all arch specific PF paths
+ * and g-u-p
+ */
+ if (ret & VM_FAULT_RETRY)
+ down_read(&vma->vm_mm->mmap_sem);
ret = VM_FAULT_SIGBUS;
+ }
return ret;
}
Patches currently in stable-queue which might be from mhocko@xxxxxxxx are
queue-4.9/mm-discard-memblock-data-later.patch
queue-4.9/mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus.patch
queue-4.9/mm-mempolicy-fix-use-after-free-when-calling-get_mempolicy.patch