linux-kernel - Re: [lkp-robot] [waitid()] 75f64d68f9: Kernel_panic-not_syncing:Attempted_to_kill

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Date:   Sun, 21 May 2017 15:19:57 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     kernel test robot <xiaolong.ye@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Christoph Hellwig <hch@....de>, LKP <lkp@...org>
Subject: Re: [lkp-robot] [waitid()] 75f64d68f9: Kernel_panic-not_syncing:Attempted_to_kill_init!exitcode=

On Sun, May 21, 2017 at 2:37 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I'm pretty sure there's a reason we added support for it on x86-32,
> because there are structures that use __u64 and fill things one entry
> at a time.

Did an "allyesconfig" build on 32-bit x86, and looked at who uses the
8-byte get_user/put_user cases:

__get_user_8:
    i915_perf_open_ioctl

__put_user_8:
    snapshot_ioctl
    sys_sendfile64
    timerfd_read
    eventfd_read
    userfaultfd_ioctl
    kpagecgroup_read
    kpagecount_read
    kpageflags_read
    __ncp_ioctl
    blkdev_ioctl
    drm_mode_object_get_properties
    drm_mode_getproperty_ioctl
    efi_test_ioctl
    params_to_user
    __rds_rdma_map

so it's not common, but both do get used.

Would any of those be changed to the unsafe versions? Maybe not. But I
think we're better off being consistent.

We basically allow all kernel integer types to be used for
put/get_user(), and the fact that some architectures don't support
them is just a quirk of that architecture, not a sign that it
shouldn't be done.

                  Linus