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    SubjectRe: [RFC][PATCH 04/20] pspace: Allow multiple instaces of the process id namespace
    Eric,

    All my commments are inline below.

    > This patch modifies the fork/exit, signal handling, and pid and
    > process group manipulating syscalls to support multiple process
    > spaces, and implements the data for allow multiple instaces of the pid
    > namespace.

    [ ... skipped .... ]

    > +extern struct pspace init_pspace;
    > +
    > +#define INVALID_PID 0x7fffffff
    <<<< what is it for?

    > +
    > +static inline int pspace_task_visible(struct pspace *pspace, struct task_struct *tsk)
    > +{
    > + return (tsk->pspace == pspace) ||
    > + ((tsk->pspace->child_reaper.pspace == pspace) &&
    > + (tsk->pspace->child_reaper.task == tsk));
    <<< the logic with child_reaper which can be somehow partly inside
    pspace... and this check is not that abvious.

    Actually I can't say your patch is cleaner somehow.
    It is very big and most of the changes are trivial, which creates an
    illusion that it is straightforward and clean.

    [ ... skipped .... ]

    > @@ -788,6 +801,16 @@ fastcall NORET_TYPE void do_exit(long co
    > panic("Attempted to kill the idle task!");
    > if (unlikely(is_init(tsk)))
    > panic("Attempted to kill init!");
    > +
    > + /*
    > + * If we are the pspace leader it is nonsense for the pspace
    > + * to continue so kill everyone else in the pspace.
    > + */
    > + if (pspace_leader(tsk)) {
    > + tsk->pspace->flags = PSPACE_EXIT;
    > + kill_pspace_info(SIGKILL, (void *)1, tsk->pspace);
    > + }
    > +
    <<<<

    1.
    flags are neither atomic nor protected with any lock.
    So if it will be used later for something else in future, there will be
    100% race. You also assigns them here, while everywhere in other places
    a bit is checked.

    2. due to 1) you code is buggy. in this respect do_exit() is not
    serialized with copy_process().

    3. due to the same 1) reason
    > + kill_pspace_info(SIGKILL, (void *)1, tsk->pspace);
    can miss a task being forked. Bang!!!

    4.
    So you are effectively inserting a code for cleaning up pspace here and
    the same is actually required for other subsystems like networking/IPC etc.
    I think you suppose that other resources are freed when the last
    reference is dropped, but to tell the truth this is a way to deadlocks.
    Because refs are put in too many places, where you can't make a real
    cleanup due to locking etc. You can't for example call syncronize_net()
    from bh, which is required for network cleanup.

    Just an another argument why containers are easier/better and why you
    will eventually end up with it.
    > if (tsk->io_context)
    > exit_io_context();
    >

    [ ... skipped ... ]

    > @@ -1147,11 +1150,55 @@ retry:
    > }
    >
    > /*
    > + * kill_pspace_info() sends a signal to all processes in a process space.
    > + * This is what kill(-1, sig) does.
    > + */
    > +
    > +int __kill_pspace_info(int sig, struct siginfo *info, struct pspace *pspace)
    > +{
    > + struct task_struct *p = NULL;
    > + int retval = 0, count = 0;
    > +
    > + for_each_process(p) {
    > + int err;
    > + /* Skip the current pspace leader */
    > + if (current_pspace_leader(p))
    > + continue;
    > +
    > + /* Skip the sender of the signal */
    > + if (p->signal == current->signal)
    > + continue;
    > +
    > + /* Skip processes outside the target process space */
    > + if (!in_pspace(pspace, p))
    > + continue;
    > +
    > + /* Finally it is a good process send the signal. */
    > + err = group_send_sig_info(sig, info, p);
    > + ++count;
    > + if (err != -EPERM)
    > + retval = err;
    <<<<
    why EPERM is ok?
    do you want to miss some tasks?
    > + }
    > + return count ? retval : -ESRCH;
    > +}
    > +

    Thanks,
    Kirill

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