Re: ->pid in dnotify

From: Jamie Lokier (jamie_at_shareable.org)
Date: 08/29/03

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    Date:	Thu, 28 Aug 2003 23:44:38 +0100
To: Ulrich Drepper <drepper@redhat.com>

    Ulrich Drepper wrote:
    > Also keep in mind that threads can go away while the process (and
    > therefore file descriptor) remain. And the ID of the thread can be
    > reused

    The problem of owner churn goes beyond threads - fds can be passed to
    other process and outlive the original thread or process which created
    them. Changing ->pid to ->tgid doesn't fix this.

    Using ->tgid in dnotify is at least consistent with fcntl_setlease()
    in locks.c, and the call to f_setown() in futex.c.

    Unfortunately I can think of a few situations where you would want the
    signal delivered to one thread, but none where you'd want it delivered
    to a whole process (same for dnotify and setlease).

    Userspace can change the pid straight after to ->pid using
    fcntl(fd,F_SETOWN,...), but that leaves a time window where a thread
    creates a dnotify or lease, and the signal will be delivered
    process-wide until the thread can direct it to itself.

    -- Jamie
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