4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Michal Hocko <mho...@suse.com>
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-mho...@kernel.org
Fixes: 3f70dc38cec2 ("mm: make sure that kthreads will not refault oom reaped
memory")
Reported-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
Signed-off-by: Michal Hocko <mho...@suse.com>
Acked-by: David Rientjes <rient...@google.com>
Cc: Andrea Argangeli <and...@kernel.org>
Cc: "Kirill A. Shutemov" <kir...@shutemov.name>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Wenwei Tao <wenwei....@alibaba-inc.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
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;
}
