From: Tejun Heo <tj@kernel.org>
To: Tao Cui <cui.tao@linux.dev>
Cc: void@manifault.com, arighi@nvidia.com, changwoo@igalia.com,
liwanwu@kylinos.cn, usama.arif@linux.dev,
sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org, Tao Cui <cuitao@kylinos.cn>
Subject: Re: [PATCH 5/6] tools/sched_ext: scx_flatcg: Don't strand a cgroup on the ENQ_RACE path
Date: Thu, 12 Nov 2026 07:34:37 -1000 [thread overview]
Message-ID: <5ee521022dea895eafcda3124d7b00ad@kernel.org> (raw)
In-Reply-To: <20261112130934.563321-6-cui.tao@linux.dev>
Hello, Tao.
On Thu, Nov 12, 2026 at 09:09:33PM +0800, Tao Cui wrote:
> Instead of bailing out, wait for the picker to resolve and retry:
> grabbing the node when it's stashed back, or bailing out when the
> picker has re-added the cgroup to the rbtree. Exhausted retries mean
> the cgroup is in the common cases either going away with its node
> dropped or already back on the rbtree; a narrow window with the picker
> still holding the node in flight can strand the cgroup the same way
> the unpatched code does, at a rate orders of magnitude below stock.
This doesn't actually fix the race. I can still reproduce the stall with the
patch applied.
Maybe just add a comment noting the race? scx_flatcg isn't expected to be
used for actual usage anyway, and things like this can be done a lot better
now using arena data structures.
Thanks.
--
tejun
next prev parent reply other threads:[~2026-11-12 17:34 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-12 13:09 [PATCH 0/6] sched_ext: fix kfunc, sub-sched, flatcg and idle-mask issues Tao Cui
2026-11-12 13:09 ` [PATCH 1/6] sched_ext: Reject DSQ iterator kfuncs in tracing programs Tao Cui
2026-11-12 17:34 ` Tejun Heo
2026-11-12 13:09 ` [PATCH 2/6] sched_ext: Make scx_bpf_cid_node() a benign lookup for invalid cids Tao Cui
2026-11-12 17:34 ` Tejun Heo
2026-11-12 13:09 ` [PATCH 3/6] sched_ext: Return -EBUSY from a pre-init scx_bpf_sub_caps() read Tao Cui
2026-11-12 17:34 ` Tejun Heo
2026-11-12 13:09 ` [PATCH 4/6] sched_ext: Reject cid_online/cid_offline on sub-schedulers Tao Cui
2026-11-12 17:34 ` Tejun Heo
2026-11-12 13:09 ` [PATCH 5/6] tools/sched_ext: scx_flatcg: Don't strand a cgroup on the ENQ_RACE path Tao Cui
2026-11-12 17:34 ` Tejun Heo [this message]
2026-11-12 13:09 ` [PATCH 6/6] sched_ext: Clear the built-in idle masks on CPU hotplug transitions Tao Cui
2026-11-12 17:34 ` Tejun Heo
2026-11-12 17:34 ` [PATCH 0/6] sched_ext: fix kfunc, sub-sched, flatcg and idle-mask issues Tejun Heo
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