[Devel] Re: [RFC][PATCH 06/14] Populate pid_nrs list with entry for init-pid-ns

[Eric W. Biederman]

sukadev at us.ibm.com writes:

> From: Cedric Le Goater <clg at fr.ibm.com>
> Subject: [RFC][PATCH 06/14] Populate pid_nrs list with entry for init-pid-ns
>
> Create/destroy the pid->pid_nrs list - when allocating/freeing  a struct pid.
> The pid_nrs list contains just a single struct pid_nr for now, (corresponding
> to init-pid-ns). 
>
> To enable finding a process based on any of its pid_t values, replace the
> use struct pid_nr, rather than struct pid, in the pid_hash table. 
>
> Finally, reimplement find_pid() and pid_nr() based on the pid_nrs list.
>
> Changelog:
> 	- [Serge Hallyn's comment]: Add comments on what pid->lock protects
> 	  and that pid->nr will eventually go away.
> 	- [Eric Biederman and containers list comments]: Reworked patches
> 	  to drop support for unsharing pid namespace and to replace
> 	  struct pid with struct pid_nr in the pid_hash table.
>
> Signed-off-by: Cedric Le Goater <clg at fr.ibm.com>
> Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> ---
>  include/linux/pid.h |    9 ------
>  kernel/pid.c | 73 ++++++++++++++++++++++++++++++++++------------------
>  2 files changed, 50 insertions(+), 32 deletions(-)
>

> @@ -242,50 +247,70 @@ struct pid_nr *alloc_pid_nr(struct pid_n
>  	 */
>  	pid_nr->pid = pid;
>
> +	spin_lock_irq(&pidmap_lock);
> +	hlist_add_head_rcu(&pid_nr->pid_chain, &pid_hash[pid_hashfn(nr)]);
> +	spin_unlock_irq(&pidmap_lock);
> +

Hmm.  I think we really need to hash in some of the bits of the
pid_namespace so processes with identical pids don't get put on
the same hash chain.  It isn't critical but it is a good idea.

Eric
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