Date:   Wed, 15 Dec 2021 15:49:44 +0100
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     Waiman Long <longman@redhat.com>
Cc:     Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <shuah@kernel.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kselftest@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>, Phil Auld <pauld@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH v9 3/7] cgroup/cpuset: Refining features and constraints
 of a partition
Message-ID: <20211215144944.GE16798@blackbody.suse.cz>
References: <20211205183220.818872-1-longman@redhat.com>
 <20211205183220.818872-4-longman@redhat.com>
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On Sun, Dec 05, 2021 at 01:32:16PM -0500, Waiman Long <longman@redhat.com> wrote:
> @@ -1455,34 +1450,16 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp)
>  			switch (parent->partition_root_state) {
> [...]
> -
>  			case PRS_ENABLED:
> -				if (update_parent_subparts_cpumask(cp, partcmd_update, NULL, tmp))
> -					update_tasks_cpumask(parent);
> +				update_parent = true;
> [...]
> +		if (update_parent) {
> +			if (update_parent_subparts_cpumask(cp, partcmd_update, NULL, tmp))
> +				update_tasks_cpumask(parent);
> +			/*
> +			 * The cpuset partition_root_state may be changed
> +			 * to PRS_ERROR. Capture it.
> +			 */
> +			new_prs = cp->partition_root_state;
> +		}

IIUC, this ensures that when a parent becomes partition root again, this
would propagate downwards to invalidated children. 

However, the documentation says:

> +       Changing a partition root (valid or invalid) to "member" is
> +       always allowed.  If there are child partition roots underneath
> +       it, they will become invalid and unrecoverable.  So care must
> +       be taken to double check for this condition before disabling
> +       a partition root.

I.e. it suggests a child can be trapped in the unrecoverable state (i.e.
not fixable by writing into cpuset.cpus.partition).
But this does not happen, right?

Michal