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    SubjectRe: + remove-the-likelypid-check-in-copy_process.patch added to -mm tree
    On 03/17, Oleg Nesterov wrote:
    >
    > > Well the initial kernel process does not have a struct pid so when
    > > it's children start doing:
    > > attach_pid(p, PIDTYPE_PGID, task_group(p));
    > > attach_pid(p, PIDTYPE_SID, task_session(p));
    > > We will get an oops.
    >
    > So far this is the only reason to have init_struct_pid. Because the
    > boot CPU (swapper) forks, right?

    Damn. I am afraid I was not clear again :) Not init_struct_pid, but

    + .pids = { \
    + [PIDTYPE_PID] = INIT_PID_LINK(PIDTYPE_PID), \
    + [PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID), \
    + [PIDTYPE_SID] = INIT_PID_LINK(PIDTYPE_SID), \
    + }, \

    for INIT_TASK().

    > > So a dummy unhashed struct pid was added for the idle threads.
    > > Allowing several special cases in the code to be removed.
    > >
    > > With that chance the previous special case to force the idle thread
    > > init session 1 pgrp 1 no longer works because attach_pid no longer
    > > looks at the pid value but instead at the struct pid pointers.
    > >
    > > So we had to add the __set_special_pids() to continue to keep init
    > > in session 1 pgrp 1. Since /sbin/init calls setsid() that our setting
    > > the sid and the pgrp may not be strictly necessary. Still is better
    > > to not take any chances.
    >
    > Yes, yes, I see. But my (very unclear, sorry) question was: shouldn't we
    > change INIT_SIGNALS then? /sbin/init inherits ->pgrp == ->_session == 1,
    > in that case __set_special_pids(1,1) does nothing.

    ... and thus /sbin/init remains attached to the .pids above, no?

    Oleg.

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