From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3915148C3FA for ; Mon, 12 Oct 2026 12:58:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791809922; cv=none; b=oGhqBGux+3bmkXUogRi3z+XVI+cs2Vidi97EMzETTEN2tLHPKAcoZZQ+LNqYnjjx/ntApDGVMqVKv83fSqWEkUXltA7GHwnETPTSVGmw044gvjvZSovNj9JwwpxdTS7ixAplit7xpPltOpQslRfl4A8DAatuSMNGN+e5Ew2x3g4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791809922; c=relaxed/simple; bh=ESROTfixozIYi1RM82dQ/LIoK9EPa79Tyz6LKhadMb8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=d3K/qFxfmer7hbmQ3oTDkb8EQb9Wbd/dclYn74hPLFVQbOR9NB4HMRwHCPLef35sqCYy9qn0yWY0b1L4PtHuqMuVzFzToVaq21Diqw9OaloBo51TT+YfFBjzeiyVPqRxrO6bGsGG8hCOl1Y0gBS7QsL3Uaj8PD9t7RH0iQ+3kyQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=b23rQ7vp; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="b23rQ7vp" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 01E1D1655; Mon, 12 Oct 2026 05:58:37 -0700 (PDT) Received: from [10.0.128.106] (e127648.arm.com [10.0.128.106]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8A2C63F66F; Mon, 12 Oct 2026 05:58:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1791809920; bh=ESROTfixozIYi1RM82dQ/LIoK9EPa79Tyz6LKhadMb8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=b23rQ7vpgLO0fW36fsrG0oxZFbV/vJuoQrH51i+gfEG5CafNxRtJ1FZFV8K/LtV03 iqOwR0VWmRJZZHOQ3N2z8RcB1wdWHACEeElveuXUoLNjdT/Jfr82OUyNVZptvRuVV3 wCdwdSqR9yt06QOSZWreRUpBnjV1lZnh9pbwdPNA= Message-ID: Date: Mon, 12 Oct 2026 13:58:36 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] sched/fair: remove dead code on enqueue_task_fair() To: Kayra Cizmeci , peterz@infradead.org, Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak Cc: linux-kernel@vger.kernel.org References: <20260911124256.GZ776954@noisy.programming.kicks-ass.net> <20260911160253.1249960-1-kayracizmeci@gmail.com> Content-Language: en-US From: Christian Loehle In-Reply-To: <20260911160253.1249960-1-kayracizmeci@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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 ]---