Re: [PATCH v11 5/9] Reimplement RLIMIT_MSGQUEUE on top of ucounts

[Alexey Gladkov]

On Thu, Aug 19, 2021 at 10:10:26AM -0500, Eric W. Biederman wrote:
> Alexey Gladkov <legion@xxxxxxxxxx> writes:
> 
> > On Tue, Aug 17, 2021 at 10:47:14AM -0500, Eric W. Biederman wrote:
> >> "Ma, XinjianX" <xinjianx.ma@xxxxxxxxx> writes:
> >> 
> >> > Hi Alexey,
> >> >
> >> > When lkp team run kernel selftests, we found after these series of patches, testcase mqueue: mq_perf_tests
> >> > in kselftest failed with following message.
> >> 
> >> Which kernel was this run against?
> >> 
> >> Where can the mq_perf_tests that you ran and had problems with be found?
> >> 
> >> During your run were you using user namespaces as part of your test
> >> environment?
> >> 
> >> The error message too many files corresponds to the error code EMFILES
> >> which is the error code that is returned when the rlimit is reached.
> >> 
> >> One possibility is that your test environment was run in a user
> >> namespace and so you wound up limited by rlimit of the user who created
> >> the user namespace at the point of user namespace creation. 
> >> 
> >> At this point if you can give us enough information to look into this
> >> and attempt to reproduce it that would be appreciated.
> >
> > I was able to reproduce it on master without using user namespace.
> > I suspect that the maximum value is not assigned here [1]:
> >
> > set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MSGQUEUE, task_rlimit(&init_task, RLIMIT_MSGQUEUE));
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/fork.c#n832
> 
> The rlimits for init_task are set to INIT_RLIMITS.
> In INIT_RLIMITS RLIMIT_MSGQUEUE is set to MQ_MAX_BYTES
> 
> So that definitely means that as the code is current constructed the
> rlimit can not be effectively raised.
> 
> So it looks like we are just silly and preventing the initial rlimits
> from being raised.
> 
> So we probably want to do something like:

Damn, you are faster than me! :)

> diff --git a/kernel/fork.c b/kernel/fork.c
> index bc94b2cc5995..557ce0083ba3 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -825,13 +825,13 @@ void __init fork_init(void)
>  	init_task.signal->rlim[RLIMIT_SIGPENDING] =
>  		init_task.signal->rlim[RLIMIT_NPROC];
>  
> +	/* For non-rlimit ucounts make their default limit max_threads/2 */
>  	for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++)
>  		init_user_ns.ucount_max[i] = max_threads/2;
>  
> -	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_NPROC, task_rlimit(&init_task, RLIMIT_NPROC));
> -	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MSGQUEUE, task_rlimit(&init_task, RLIMIT_MSGQUEUE));
> -	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_SIGPENDING, task_rlimit(&init_task, RLIMIT_SIGPENDING));
> -	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MEMLOCK, task_rlimit(&init_task, RLIMIT_MEMLOCK));
> +	/* In init_user_ns default rlimit to be the only limit */
> +	for (; i < UCOUNT_COUNTS; i++)
> +		set_rlimit_ucount_max(&init_user_ns, i, RLIMIT_INFINITY);

s/RLIMIT_INFINITY/RLIM_INFINITY/

>  
>  #ifdef CONFIG_VMAP_STACK
>  	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
> 

Acked-by: Alexey Gladkov <legion@xxxxxxxxxx>

I cannot complete this test on my laptop. On 4Gb, the test ends with
oom-killer. But with this patch, the test definitely passes the moment of
the previous fall.

-- 
Rgrds, legion