linux-kernel - Re: [RFC PATCH v2 3/3] mm, oom: hand over MMF_OOM_SKIP to exit path if it is guranteed to finish

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Date:   Tue, 30 Oct 2018 13:45:22 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Roman Gushchin <guro@...com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH v2 3/3] mm, oom: hand over MMF_OOM_SKIP to exit path if it is guranteed to finish

Michal Hocko wrote:
> @@ -3156,6 +3166,13 @@ void exit_mmap(struct mm_struct *mm)
>                 vma = remove_vma(vma);
>         }
>         vm_unacct_memory(nr_accounted);
> +
> +       /*
> +        * Now that the full address space is torn down, make sure the
> +        * OOM killer skips over this task
> +        */
> +       if (oom)
> +               set_bit(MMF_OOM_SKIP, &mm->flags);
>  }
> 
>  /* Insert vm structure into process list sorted by address

I don't like setting MMF_OOF_SKIP after remove_vma() loop. 50 users might
call vma->vm_ops->close() from remove_vma(). Some of them are doing fs
writeback, some of them might be doing GFP_KERNEL allocation from
vma->vm_ops->open() with a lock also held by vma->vm_ops->close().

I don't think that waiting for completion of remove_vma() loop is safe.
And my patch is safe.

 drivers/android/binder.c                          |    2 +-
 drivers/gpu/drm/drm_gem_cma_helper.c              |    2 +-
 drivers/gpu/drm/drm_vm.c                          |    8 ++++----
 drivers/gpu/drm/gma500/framebuffer.c              |    2 +-
 drivers/gpu/drm/gma500/psb_drv.c                  |    2 +-
 drivers/gpu/drm/i915/i915_drv.c                   |    2 +-
 drivers/gpu/drm/ttm/ttm_bo_vm.c                   |    2 +-
 drivers/gpu/drm/udl/udl_drv.c                     |    2 +-
 drivers/gpu/drm/v3d/v3d_drv.c                     |    2 +-
 drivers/gpu/drm/vc4/vc4_drv.c                     |    2 +-
 drivers/gpu/drm/vgem/vgem_drv.c                   |    2 +-
 drivers/gpu/drm/vkms/vkms_drv.c                   |    2 +-
 drivers/gpu/drm/xen/xen_drm_front.c               |    2 +-
 drivers/hwtracing/intel_th/msu.c                  |    2 +-
 drivers/hwtracing/stm/core.c                      |    2 +-
 drivers/infiniband/core/uverbs_main.c             |    2 +-
 drivers/infiniband/sw/rdmavt/mmap.c               |    2 +-
 drivers/infiniband/sw/rxe/rxe_mmap.c              |    2 +-
 drivers/media/common/videobuf2/videobuf2-memops.c |    2 +-
 drivers/media/pci/meye/meye.c                     |    2 +-
 drivers/media/platform/omap/omap_vout.c           |    2 +-
 drivers/media/usb/stkwebcam/stk-webcam.c          |    2 +-
 drivers/media/v4l2-core/videobuf-dma-contig.c     |    2 +-
 drivers/media/v4l2-core/videobuf-dma-sg.c         |    2 +-
 drivers/media/v4l2-core/videobuf-vmalloc.c        |    2 +-
 drivers/misc/genwqe/card_dev.c                    |    2 +-
 drivers/misc/mic/scif/scif_mmap.c                 |    2 +-
 drivers/misc/sgi-gru/grufile.c                    |    2 +-
 drivers/rapidio/devices/rio_mport_cdev.c          |    2 +-
 drivers/staging/comedi/comedi_fops.c              |    2 +-
 drivers/staging/media/zoran/zoran_driver.c        |    2 +-
 drivers/staging/vme/devices/vme_user.c            |    2 +-
 drivers/usb/core/devio.c                          |    2 +-
 drivers/usb/mon/mon_bin.c                         |    2 +-
 drivers/video/fbdev/omap2/omapfb/omapfb-main.c    |    2 +-
 drivers/xen/gntalloc.c                            |    2 +-
 drivers/xen/gntdev.c                              |    2 +-
 drivers/xen/privcmd-buf.c                         |    2 +-
 drivers/xen/privcmd.c                             |    2 +-
 fs/9p/vfs_file.c                                  |    2 +-
 fs/fuse/file.c                                    |    2 +-
 fs/kernfs/file.c                                  |    2 +-
 include/linux/mm.h                                |    2 +-
 ipc/shm.c                                         |    2 +-
 kernel/events/core.c                              |    2 +-
 kernel/relay.c                                    |    2 +-
 mm/hugetlb.c                                      |    2 +-
 mm/mmap.c                                         |   14 +++++++-------
 net/packet/af_packet.c                            |    2 +-
 sound/core/pcm_native.c                           |    4 ++--
 sound/usb/usx2y/us122l.c                          |    2 +-
 sound/usb/usx2y/usx2yhwdeppcm.c                   |    2 +-
 52 files changed, 62 insertions(+), 62 deletions(-)