[Devel] Re: [RFC/PATCH 1/8]: CGroup Files: Add locking mode to cgroups control files

[Li Zefan]

menage at google.com wrote:
> Different cgroup files have different stability requirements of the
> cgroups framework while the handler is running; currently most
> subsystems that don't have their own internal synchronization just
> call cgroup_lock()/cgroup_unlock(), which takes the global cgroup_mutex.
> 
> This patch introduces a range of locking modes that can be requested
> by a control file; currently these are all implemented internally by
> taking cgroup_mutex, but expressing the intention will make it simpler
> to move to a finer-grained locking scheme in the future.
> 
> Signed-off-by: Paul Menage<menage at google.com>
> 

This patch series looks good to me. I've reviewed those patches and didn't
see anything wrong, except a little comments below.

[..snap..]

> -static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
> -				struct file *file,
> -				const char __user *userbuf,
> -				size_t nbytes, loff_t *unused_ppos)
> +
> +
> +/**
> + * cgroup_file_lock(). Helper for cgroup read/write methods.
> + * @cgrp:  the cgroup being acted on
> + * @cft:   the control file being written to or read from
> + * *write: true if the access is a write access.

s/*write/@write

[..snip..]

>  
>  static ssize_t cgroup_common_file_read(struct cgroup *cgrp,
> @@ -1518,16 +1580,21 @@ static ssize_t cgroup_file_read(struct f
>  	struct cftype *cft = __d_cft(file->f_dentry);
>  	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
>  
> -	if (!cft || cgroup_is_removed(cgrp))
> +	if (cgroup_is_removed(cgrp))
>  		return -ENODEV;
>  

This check seems redundant now.

> -	if (cft->read)
> -		return cft->read(cgrp, cft, file, buf, nbytes, ppos);
> -	if (cft->read_u64)
> -		return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
> -	if (cft->read_s64)
> -		return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
> -	return -EINVAL;
> +	if (cft->read) {
> +		/* Raw read function - no extra processing by cgroups */
> +		ssize_t retval = cgroup_file_lock(cgrp, cft, 0);
> +		if (!retval)
> +			retval = cft->read(cgrp, cft, file, buf, nbytes, ppos);
> +		cgroup_file_unlock(cgrp, cft, 0);
> +		return retval;
> +	}
> +	if (cft->read_u64 || cft->read_s64)
> +		return cgroup_read_X64(cgrp, cft, file, buf, nbytes, ppos);
> +	else
> +		return -EINVAL;
>  }

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