linux-kernel - Re: [PATCH 2/2] cpuset: Call set_cpus_allowed

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Message-ID: <Y+FhRW59h+h1bTcr@slm.duckdns.org>
Date:   Mon, 6 Feb 2023 10:21:25 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Peter Zijlstra <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org
Subject: Re: [PATCH 2/2] cpuset: Call set_cpus_allowed_ptr() with appropriate
 mask for task

On Tue, Jan 31, 2023 at 10:17:19PM +0000, Will Deacon wrote:
> set_cpus_allowed_ptr() will fail with -EINVAL if the requested
> affinity mask is not a subset of the task_cpu_possible_mask() for the
> task being updated. Consequently, on a heterogeneous system with cpusets
> spanning the different CPU types, updates to the cgroup hierarchy can
> silently fail to update task affinities when the effective affinity
> mask for the cpuset is expanded.
> 
> For example, consider an arm64 system with 4 CPUs, where CPUs 2-3 are
> the only cores capable of executing 32-bit tasks. Attaching a 32-bit
> task to a cpuset containing CPUs 0-2 will correctly affine the task to
> CPU 2. Extending the cpuset to CPUs 0-3, however, will fail to extend
> the affinity mask of the 32-bit task because update_tasks_cpumask() will
> pass the full 0-3 mask to set_cpus_allowed_ptr().
> 
> Extend update_tasks_cpumask() to take a temporary 'cpumask' paramater
> and use it to mask the 'effective_cpus' mask with the possible mask for
> each task being updated.
> 
> Fixes: 431c69fac05b ("cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()")
> Signed-off-by: Will Deacon <will@...nel.org>

Applied to cgroup/for-6.2-fixes.

Thanks.

-- 
tejun