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[PATCH 4.12 18/41] mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS

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4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michal Hocko <mhocko@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-mhocko@kernel.org
Fixes: 3f70dc38cec2 ("mm: make sure that kthreads will not refault oom reaped memory")
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Andrea Argangeli <andrea@kernel.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Wenwei Tao <wenwei.tww@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/memory.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3882,8 +3882,18 @@ 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;
 }

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[PATCH 4.12 00/41] 4.12.9-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 28/41] perf/x86: Fix RDPMC vs. mm_struct tracking Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 09/41] md: fix test in md_write_start() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 31/41] x86/elf: Remove the unnecessary ADDR_NO_RANDOMIZE checks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 19/41] mm/cma_debug.c: fix stack corruption due to sprintf usage Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 21/41] mm/vmalloc.c: dont unconditonally use __GFP_HIGHMEM Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 02/41] parisc: pci memory bar assignment fails with 64bit kernels on dino/cujo Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 10/41] md: always clear ->safemode when md_check_recovery gets the mddev lock. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 25/41] blk-mq-pci: add a fallback when pci_irq_get_affinity returns NULL Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 05/41] drm/i915: Perform an invalidate prior to executing golden renderstate Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 22/41] mm: revert x86_64 and arm64 ELF_ET_DYN_BASE base changes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 01/41] audit: Fix use after free in audit_remove_watch_rule() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 27/41] xen-blkfront: use a right index when checking requests Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 18/41] mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 32/41] irqchip/atmel-aic: Fix unbalanced of_node_put() in aic_common_irq_fixup() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  [PATCH 4.12 29/41] x86/asm/64: Clear AC on NMI entries Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:30 +0200
  Re: [PATCH 4.12 00/41] 4.12.9-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-08-23 02:40 +0200
    Re: [PATCH 4.12 00/41] 4.12.9-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-23 02:50 +0200

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