From: Christian Loehle <christian.loehle@arm.com>
To: Kayra Cizmeci <kayracizmeci@gmail.com>,
peterz@infradead.org, Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>,
K Prateek Nayak <kprateek.nayak@amd.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] sched/fair: remove dead code on enqueue_task_fair()
Date: Mon, 12 Oct 2026 13:58:36 +0100 [thread overview]
Message-ID: <fd3f9d83-cb5b-496b-b7c1-b40f31cf795e@arm.com> (raw)
In-Reply-To: <20260911160253.1249960-1-kayracizmeci@gmail.com>
On 9/11/26 17:02, Kayra Cizmeci wrote:
> cfs_rq->curr == se path on enqueue_task_fair() seems to be unachievable.
Sashiko disagrees so I had a look and indeed cfs_rq unthrottling reaches this:
https://sashiko.dev/#/patchset/179033365207.2819794.11851486661940182495.tip-bot2%40tip-bot2
See the splat below.
I'm afraid we need to revert
819224e506bc ("sched/fair: Remove dead code on enqueue_task_fair()")
on tip/sched/core.
I guess it's non-obvious enough to deserve a comment...
[ 95.833742] ------------[ cut here ]------------
[ 95.833749] WARNING: kernel/sched/fair.c:8028 at enqueue_task_fair+0x7a8/0xa40, CPU#10: python3/6699
[ 95.847486] Modules linked in: qrtr 8021q garp mrp stp llc cppc_cpufreq cdns3_pci_wrap binfmt_misc nf_tables fuse dm_mod r8169
[ 95.858876] CPU: 10 UID: 0 PID: 6699 Comm: python3 Tainted: G S 7.3.0-rc1-mpam-rt-orion-20261008+ #2 PREEMPT_RT
[ 95.870517] Tainted: [S]=CPU_OUT_OF_SPEC
[ 95.874428] Hardware name: Radxa Computer (Shenzhen) Co., Ltd. Radxa Orion O6/Radxa Orion O6, BIOS 1.1.0-1 2025-12-25T02:55:53+00:00
[ 95.886324] pstate: 634000c9 (nZCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
[ 95.893275] pc : enqueue_task_fair+0x7a8/0xa40
[ 95.897705] lr : enqueue_task_fair+0x324/0xa40
[ 95.902136] sp : ffff800090323a50
[ 95.905438] x29: ffff800090323a50 x28: 0000000000000009 x27: ffffd8536a9cc5c0
[ 95.912565] x26: fffffdffbf43e1c0 x25: ffff0001fb7729c0 x24: fffffdffbf43e390
[ 95.919692] x23: 0000000000000001 x22: ffff000085d52400 x21: 0000000000000000
[ 95.926817] x20: ffff000085d52380 x19: ffff0001fb7727c0 x18: 0000000000000000
[ 95.933943] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000037d54fe0
[ 95.941069] x14: 0000000000000000 x13: ffffffffffffffff x12: ffffd8536a9cbdf8
[ 95.948195] x11: 00000000000000c0 x10: 02ae55ef2a914684 x9 : ffff00008d3511c0
[ 95.955321] x8 : 0000000000000001 x7 : 0000004100000000 x6 : ffffd8536a9cc5c0
[ 95.962442] x5 : ffff800090323ad8 x4 : ffff800090323ad8 x3 : ffff000085d527b8
[ 95.969563] x2 : 0000000000000001 x1 : ffff000085d52400 x0 : ffff000085d52400
[ 95.976689] Call trace:
[ 95.979124] enqueue_task_fair+0x7a8/0xa40 (P)
[ 95.983559] tg_unthrottle_up+0x14c/0x318
[ 95.987561] walk_tg_tree_from+0x60/0xb8
[ 95.991481] unthrottle_cfs_rq+0xa8/0x204
[ 95.995484] tg_set_bandwidth+0x36c/0x4c4
[ 95.999485] cpu_max_write+0xc8/0x130
[ 96.003138] cgroup_file_write+0xa4/0x194
[ 96.007150] kernfs_fop_write_iter+0x130/0x1fc
[ 96.011598] vfs_write+0x228/0x358
[ 96.015001] ksys_write+0x6c/0x104
[ 96.018395] __arm64_sys_write+0x18/0x24
[ 96.022309] invoke_syscall+0x54/0x110
[ 96.026051] el0_svc_common.constprop.0+0x40/0xe0
[ 96.030744] do_el0_svc+0x1c/0x28
[ 96.034048] el0_svc+0x38/0x260
[ 96.037183] el0t_64_sync_handler+0xa0/0xe4
[ 96.041357] el0t_64_sync+0x17c/0x180
[ 96.045011] ---[ end trace 0000000000000000 ]---
next prev parent reply other threads:[~2026-10-12 12:58 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-24 12:52 [PATCH 1/2] sched/fair: reuse the ENQUEUE_DELAYED calculation in enqueue_task_fair() Kayra Cizmeci
2026-08-24 12:52 ` [PATCH 2/2] sched/fair: avoid recalculating curr status in place_entity() and requeue_delayed_entity() Kayra Cizmeci
2026-08-26 10:15 ` [PATCH v2 0/2] sched/fair: reduce repeated work in enqueue path Kayra Cizmeci
2026-08-26 10:15 ` [PATCH v2 1/2] sched/fair: reuse the ENQUEUE_DELAYED calculation in enqueue_task_fair() Kayra Cizmeci
2026-08-26 10:41 ` K Prateek Nayak
2026-08-26 18:44 ` Kayra Cizmeci
2026-09-07 16:05 ` [PATCH] sched/fair: Remove unused autogroup.h include Kayra Cizmeci
2026-09-07 16:14 ` [PATCH v2 1/2] sched/fair: reuse the ENQUEUE_DELAYED calculation in enqueue_task_fair() Kayra Cizmeci
2026-08-26 10:15 ` [PATCH v2 2/2] sched/fair: avoid recalculating curr status in place_entity() and requeue_delayed_entity() Kayra Cizmeci
2026-09-11 10:57 ` Kayra Cizmeci
2026-09-11 12:19 ` Vincent Guittot
2026-09-11 13:10 ` Kayra Cizmeci
2026-09-11 12:42 ` Peter Zijlstra
2026-09-11 14:08 ` Kayra Cizmeci
2026-09-11 16:02 ` [PATCH v3] sched/fair: remove dead code on enqueue_task_fair() Kayra Cizmeci
2026-10-12 12:58 ` Christian Loehle [this message]
2026-10-12 13:33 ` Kayra Cizmeci
2026-10-12 14:02 ` Peter Zijlstra
2026-10-12 14:15 ` Kayra Cizmeci
2026-10-12 14:59 ` Christian Loehle
2026-10-13 11:58 ` Peter Zijlstra
2026-10-13 13:42 ` Kayra Cizmeci
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