Re: [PATCH] ipc,mqueue: remove limits for the amount of system-wide queues

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 09 Feb 2014 13:06:03 -0800 Davidlohr Bueso <davidlohr@hp.com> wrote:

> From: Davidlohr Bueso <davidlohr@hp.com>
> 
> Commit 93e6f119 (ipc/mqueue: cleanup definition names and locations) added
> global hardcoded limits to the amount of message queues that can be created.
> While these limits are per-namespace, reality is that it ends up breaking
> userspace applications. Historically users have, at least in theory, been able
> to create up to INT_MAX queues, and limiting it to just 1024 is way too low
> and dramatic for some workloads and use cases. For instance, Madars reports:
> 
> "This update imposes bad limits on our multi-process application. As our
> app uses approaches that each process opens its own set of queues (usually
> something about 3-5 queues per process). In some scenarios we might run up
> to 3000 processes or more (which of-course for linux is not a problem).
> Thus we might need up to 9000 queues or more. All processes run under one
> user."
> 
> Other affected users can be found in launchpad bug #1155695:
> https://bugs.launchpad.net/ubuntu/+source/manpages/+bug/1155695
> 
> Instead of increasing this limit, revert it entirely and fallback to the
> original way of dealing queue limits -- where once a user's resource limit
> is reached, and all memory is used, new queues cannot be created.
> 
> --- a/ipc/mq_sysctl.c
> +++ b/ipc/mq_sysctl.c
> @@ -22,6 +22,16 @@ static void *get_mq(ctl_table *table)
>  	return which;
>  }
>  
> +static int proc_mq_dointvec(ctl_table *table, int write,
> +			    void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> +	struct ctl_table mq_table;
> +	memcpy(&mq_table, table, sizeof(mq_table));
> +	mq_table.data = get_mq(table);
> +
> +	return proc_dointvec(&mq_table, write, buffer, lenp, ppos);
> +}
> +
>  static int proc_mq_dointvec_minmax(ctl_table *table, int write,
>  	void __user *buffer, size_t *lenp, loff_t *ppos)
>  {
>
> ...
>
> @@ -51,9 +59,7 @@ static ctl_table mq_sysctls[] = {
>  		.data		= &init_ipc_ns.mq_queues_max,
>  		.maxlen		= sizeof(int),
>  		.mode		= 0644,
> -		.proc_handler	= proc_mq_dointvec_minmax,
> -		.extra1		= &msg_queues_limit_min,
> -		.extra2		= &msg_queues_limit_max,
> +		.proc_handler	= proc_mq_dointvec,
>  	},

hm, afaict proc_mq_dointvec() isn't needed - proc_dointvec_minmax()
will do the right thing if ->extra1 and/or ->extra2 are NULL, so we can
still use proc_mq_dointvec_minmax().

Which has absolutely nothing at all to do with your patch, but makes me
think we could take a sharp instrument to the sysctl code...