[Devel] Re: [PATCH] attach_pid() with struct pid parameter

[Serge E. Hallyn]

Could you also add a comment above both find_attach_pid() and
attach_pid() saying they are always called with the
tasklist_lock write-held?  Keeps each patch reader from having
to go verify that...

thanks,
-serge

Quoting Sukadev Bhattiprolu (sukadev at us.ibm.com):
> 
> From: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> 
> Implement a new version of attach_pid() with a struct pid parameter and
> wrap find_attach_pid() around it. attach_pid() would also be used in
> subsequent container patches.
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> Cc: Cedric Le Goater <clg at fr.ibm.com>
> Cc: Dave Hansen <haveblue at us.ibm.com>
> Cc: Serge Hallyn <serue at us.ibm.com>
> Cc: containers at lists.osdl.org
> ---
>  include/linux/pid.h |   28 +++++++++++++++++-----------
>  kernel/pid.c        |    7 +++----
>  2 files changed, 20 insertions(+), 15 deletions(-)
> 
> Index: lx26-20-rc2-mm1/include/linux/pid.h
> ===================================================================
> --- lx26-20-rc2-mm1.orig/include/linux/pid.h	2007-01-11 04:44:06.674046656 -0800
> +++ lx26-20-rc2-mm1/include/linux/pid.h	2007-01-11 04:44:56.820423248 -0800
> @@ -72,17 +72,6 @@ extern struct task_struct *FASTCALL(get_
>  extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
> 
>  /*
> - * find_attach_pid() and detach_pid() must be called with the tasklist_lock
> - * write-held.
> - */
> -extern int FASTCALL(find_attach_pid(struct task_struct *task,
> -				enum pid_type type, int nr));
> -
> -extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
> -extern void FASTCALL(transfer_pid(struct task_struct *old,
> -				  struct task_struct *new, enum pid_type));
> -
> -/*
>   * look up a PID in the hash table. Must be called with the tasklist_lock
>   * or rcu_read_lock() held.
>   */
> @@ -94,6 +83,23 @@ extern struct pid *FASTCALL(find_pid(int
>  extern struct pid *find_get_pid(int nr);
>  extern struct pid *find_ge_pid(int nr);
> 
> +/*
> + * attach_pid(), find_attach_pid() and detach_pid() must be called with the
> + * tasklist_lock write-held.
> + */
> +extern int FASTCALL(attach_pid(struct task_struct *task, enum pid_type type,
> +				struct pid *pid));
> +
> +static inline int find_attach_pid(struct task_struct *task, enum pid_type type,
> +				int nr)
> +{
> +	return attach_pid(task, type, find_pid(nr));
> +}
> +
> +extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
> +extern void FASTCALL(transfer_pid(struct task_struct *old,
> +				  struct task_struct *new, enum pid_type));
> +
>  extern struct pid *alloc_pid(void);
>  extern void FASTCALL(free_pid(struct pid *pid));
> 
> Index: lx26-20-rc2-mm1/kernel/pid.c
> ===================================================================
> --- lx26-20-rc2-mm1.orig/kernel/pid.c	2007-01-11 04:44:06.674046656 -0800
> +++ lx26-20-rc2-mm1/kernel/pid.c	2007-01-11 04:44:56.821423096 -0800
> @@ -247,14 +247,13 @@ struct pid * fastcall find_pid(int nr)
>  }
>  EXPORT_SYMBOL_GPL(find_pid);
> 
> -int fastcall find_attach_pid(struct task_struct *task, enum pid_type type,
> -				int nr)
> +int fastcall attach_pid(struct task_struct *task, enum pid_type type,
> +				struct pid *pid)
>  {
>  	struct pid_link *link;
> -	struct pid *pid;
> 
>  	link = &task->pids[type];
> -	link->pid = pid = find_pid(nr);
> +	link->pid = pid;
>  	hlist_add_head_rcu(&link->node, &pid->tasks[type]);
> 
>  	return 0;
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