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    SubjectRe: [lkp-robot] [blk] 47e0fb461f: BUG:unable_to_handle_kernel
    On Thu, Sep 21 2017, kernel test robot wrote:

    > FYI, we noticed the following commit:
    >
    > commit: 47e0fb461fca1a68a566c82fcc006cc787312d8c ("blk: make the bioset rescue_workqueue optional.")
    > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
    >
    > in testcase: trinity
    > with following parameters:
    >
    > runtime: 300s
    >
    > test-description: Trinity is a linux system call fuzz tester.
    > test-url: http://codemonkey.org.uk/projects/trinity/
    >
    >
    > on test machine: qemu-system-x86_64 -enable-kvm -cpu IvyBridge -m 420M
    >
    > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):

    Interesting.
    I cannot see how that bug could be caused by that patch.

    I think it is crashing in
    static inline bool ata_is_host_link(const struct ata_link *link)
    {
    return link == &link->ap->link || link == link->ap->slave_link;
    }
    from
    static inline int ata_link_max_devices(const struct ata_link *link)
    {
    if (ata_is_host_link(link) && link->ap->flags & ATA_FLAG_SLAVE_POSS)
    return 2;
    return 1;
    }
    from ata_dev_next().

    I think %rdi holds link->ap, so the "link->ap->slave_link" dereference
    causes the crash.

    link->ap seems to be initialized quite early, and never cleared, so I
    don't know how it could be NULL...

    Confused.

    Thanks,
    NeilBrown
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