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From: Tejun Heo <tj@kernel.org>
To: Michal Blaszczyk <michalblk@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	David Vernet <void@manifault.com>,
	Andrea Righi <arighi@nvidia.com>,
	Changwoo Min <changwoo@igalia.com>,
	Kuba Piecuch <jpiecuch@google.com>,
	sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] sched: Lift cgroup update locking to core to prevent CFS/SCX divergence
Date: Mon, 31 Aug 2026 12:36:29 -1000	[thread overview]
Message-ID: <e9cd7bd7c303b57d8716c4a8cab35058@kernel.org> (raw)
In-Reply-To: <20260824074913.2468177-1-michalblk@google.com>

Hello,

On Mon, Aug 24, 2026 at 07:49:13AM +0000, Michal Blaszczyk wrote:
> Concurrent writes to cgroup control files (such as cpu.shares or
> cpu.weight) can lead to state divergence between CFS and SCX.
>
> For instance, in cpu_shares_write_u64(), the CFS update is serialized
> by shares_mutex (internal to fair.c), but this lock is dropped before
> scx_group_set_weight() is called. The latter only acquires a read
> semaphore (scx_cgroup_ops_rwsem), allowing multiple threads to evaluate
> and act on the sched_ext update concurrently.
...
> Fixes: 819513666966 ("sched_ext: Add cgroup support")
> Signed-off-by: Michal Blaszczyk <michalblk@google.com>

Acked-by: Tejun Heo <tj@kernel.org>

Peter, would you mind picking this up?

Thanks.

--
tejun

      parent reply	other threads:[~2026-08-31 22:36 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-08-24  7:49 Michal Blaszczyk
2026-08-24 11:24 ` Andrea Righi
2026-08-31 22:36 ` Tejun Heo [this message]

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