linux-kernel - Re: [net PATCH v2 1/2] net: netprio: fix files lock and remove useless d

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Message-ID: <20120814125623.GB18731@hmsreliant.think-freely.org>
Date:	Tue, 14 Aug 2012 08:56:24 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	John Fastabend <john.r.fastabend@...el.com>
Cc:	viro@...IV.linux.org.uk, netdev@...r.kernel.org,
	davem@...emloft.net, linux-kernel@...r.kernel.org, joe@...ches.com
Subject: Re: [net PATCH v2 1/2] net: netprio: fix files lock and remove
 useless d_path bits

On Mon, Aug 13, 2012 at 07:43:21PM -0700, John Fastabend wrote:
> Add lock to prevent a race with a file closing and also remove
> useless and ugly sscanf code. The extra code was never needed
> and the case it supposedly protected against is in fact handled
> correctly by sock_from_file as pointed out by Al Viro.
> 
> CC: Neil Horman <nhorman@...driver.com>
> Reported-by: Al Viro <viro@...IV.linux.org.uk>
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> ---
> 
>  net/core/netprio_cgroup.c |   22 ++++------------------
>  1 files changed, 4 insertions(+), 18 deletions(-)
> 
> diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
> index ed0c043..f65dba3 100644
> --- a/net/core/netprio_cgroup.c
> +++ b/net/core/netprio_cgroup.c
> @@ -277,12 +277,6 @@ out_free_devname:
>  void net_prio_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
>  {
>  	struct task_struct *p;
> -	char *tmp = kzalloc(sizeof(char) * PATH_MAX, GFP_KERNEL);
> -
> -	if (!tmp) {
> -		pr_warn("Unable to attach cgrp due to alloc failure!\n");
> -		return;
> -	}
>  
>  	cgroup_taskset_for_each(p, cgrp, tset) {
>  		unsigned int fd;
> @@ -296,32 +290,24 @@ void net_prio_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
>  			continue;
>  		}
>  
> -		rcu_read_lock();
> +		spin_lock(&files->file_lock);
>  		fdt = files_fdtable(files);
>  		for (fd = 0; fd < fdt->max_fds; fd++) {
> -			char *path;
>  			struct file *file;
>  			struct socket *sock;
> -			unsigned long s;
> -			int rv, err = 0;
> +			int err;
>  
>  			file = fcheck_files(files, fd);
>  			if (!file)
>  				continue;
>  
> -			path = d_path(&file->f_path, tmp, PAGE_SIZE);
> -			rv = sscanf(path, "socket:[%lu]", &s);
> -			if (rv <= 0)
> -				continue;
> -
>  			sock = sock_from_file(file, &err);
> -			if (!err)
> +			if (sock)
>  				sock_update_netprioidx(sock->sk, p);
>  		}
> -		rcu_read_unlock();
> +		spin_unlock(&files->file_lock);
>  		task_unlock(p);
>  	}
> -	kfree(tmp);
>  }
>  
>  static struct cftype ss_files[] = {
> 
This looks ok to me, but I've already shown my inability to review code that
interfaces with VFS.  Al, what do you think?

Neil

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