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    SubjectRe: [PATCH] Uprobes: Fix kernel oops with delayed_uprobe_remove()
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    Hi Oleg,

    On 11/14/18 9:36 PM, Oleg Nesterov wrote:
    > On 11/14, Ravi Bangoria wrote:
    >>
    >> syzbot reported a kernel crash with delayed_uprobe_remove():
    >> https://lkml.org/lkml/2018/11/1/1244
    >>
    >> Backtrace mentioned in the link points to a race between process
    >> exit and uprobe_unregister(). Fix it by locking delayed_uprobe_lock
    >> before calling delayed_uprobe_remove() from put_uprobe().
    >
    > The patch looks good to me, but could you update the changelog?
    >
    > Please explain that the exiting task calls uprobe_clear_state() which
    > can race with delayed_uprobe_remove(). IIUC this is the only problem
    > solved by this patch, right?

    Right. Is this better:

    There could be a race between task exit and probe unregister:

    exit_mm()
    mmput()
    __mmput() uprobe_unregister()
    uprobe_clear_state() put_uprobe()
    delayed_uprobe_remove() delayed_uprobe_remove()

    put_uprobe() is calling delayed_uprobe_remove() without taking
    delayed_uprobe_lock and thus the race sometimes results in a
    kernel crash. Fix this by taking delayed_uprobe_lock before
    calling delayed_uprobe_remove() from put_uprobe().

    Detailed crash log can be found at:
    https://lkml.org/lkml/2018/11/1/1244

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