Re: ->pid in dnotify

[Jamie Lokier]

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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