linux-kernel - Re: [PATCH 3/4] proc: task_state: move the main seq_printf() outside of rcu_read

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Date:	Thu, 13 Nov 2014 10:04:34 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Aaron Tomlin <atomlin@...hat.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Sterling Alexander <stalexan@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] proc: task_state: move the main seq_printf() outside
	of rcu_read_lock()

On Fri, Nov 07, 2014 at 09:14:51PM +0100, Oleg Nesterov wrote:
> task_state() does seq_printf() under rcu_read_lock(), but this is only
> needed for task_tgid_nr_ns() and task_numa_group_id(). We can calculate
> tgid/ngid and drop rcu lock.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> ---
>  fs/proc/array.c |   12 ++++++------
>  1 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/proc/array.c b/fs/proc/array.c
> index 7c8d9ae..800e30f 100644
> --- a/fs/proc/array.c
> +++ b/fs/proc/array.c
> @@ -158,7 +158,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
>  	struct group_info *group_info;
>  	int g;
>  	const struct cred *cred;
> -	pid_t ppid, tpid;
> +	pid_t ppid, tpid, tgid, ngid;
>  	unsigned int max_fds = 0;
> 
>  	rcu_read_lock();
> @@ -170,12 +170,16 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
>  		if (tracer)
>  			tpid = task_pid_nr_ns(tracer, ns);
>  	}
> +
> +	tgid = task_tgid_nr_ns(p, ns);
> +	ngid = task_numa_group_id(p);
>  	cred = get_task_cred(p);
> 
>  	task_lock(p);
>  	if (p->files)
>  		max_fds = files_fdtable(p->files)->max_fds;
>  	task_unlock(p);
> +	rcu_read_unlock();
> 
>  	seq_printf(m,
>  		"State:\t%s\n"
> @@ -188,10 +192,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
>  		"Gid:\t%d\t%d\t%d\t%d\n"
>  		"FDSize:\t%d\nGroups:\t",
>  		get_task_state(p),
> -		task_tgid_nr_ns(p, ns),
> -		task_numa_group_id(p),
> -		pid_nr_ns(pid, ns),
> -		ppid, tpid,
> +		tgid, ngid, pid_nr_ns(pid, ns), ppid, tpid,
>  		from_kuid_munged(user_ns, cred->uid),
>  		from_kuid_munged(user_ns, cred->euid),
>  		from_kuid_munged(user_ns, cred->suid),
> @@ -201,7 +202,6 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
>  		from_kgid_munged(user_ns, cred->sgid),
>  		from_kgid_munged(user_ns, cred->fsgid),
>  		max_fds);
> -	rcu_read_unlock();
> 
>  	group_info = cred->group_info;
>  	for (g = 0; g < group_info->ngroups; g++)
> -- 
> 1.5.5.1
> 
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