From: Michal Hocko Date: Fri, 18 Aug 2017 22:16:12 +0000 (-0700) Subject: mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=5b53a6ea886700a128b697a6fe8375340dea2c30;p=openwrt%2Fstaging%2Fblogic.git mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS 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 Signed-off-by: Michal Hocko Acked-by: David Rientjes Cc: Andrea Argangeli Cc: "Kirill A. Shutemov" Cc: Oleg Nesterov Cc: Wenwei Tao Cc: [4.9+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/memory.c b/mm/memory.c index e158f7ac6730..c717b5bcc80e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3910,8 +3910,18 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address, * 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; }