From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A18CF1D1E60 for ; Wed, 2 Oct 2024 21:08:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727903305; cv=none; b=HUO8MU9gQjyt0XvMIPGXcO4X1fqzwT42ADCyQLDQr/F1E1ag9dSjnySzfj9Fj+kmCKmSKmcBVuBT6skP9w9XUs3Du0etoYOlxBM+2e4l2DQMF4xXm8hhmitM0Sy2g3HuVDN43DK4Lhs+LTiZoDKEGn3uHzLUoAk7/a+r24r+h20= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727903305; c=relaxed/simple; bh=JY8iHEM3V4b5AtWB8ZdD25cCzC7BU/zTyXKmXkLPm7Y=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=lb9gGsPRjs3ymwNwiTTsvu9BH205Ho5R03br2FCvWKCGInIkbe1KGCv5eW1XHz59tE0ZqkUvVRTVamx+DIdq0UcPeIGlQby9MUTSGf1VKW7KmVfDAmm4e6P5KOz8jtNSoNpEkazV4LyjJDRkhfzjMaGma4zRN7sljI1WeJB/Xlk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=js1oqBaq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="js1oqBaq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA250C4CEC2; Wed, 2 Oct 2024 21:08:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1727903305; bh=JY8iHEM3V4b5AtWB8ZdD25cCzC7BU/zTyXKmXkLPm7Y=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=js1oqBaqg6DU7npcFJ3U5jCYwo2mJyVK7jg+wI4IecHTjIZYAcIc+ydgBvZGveb9j JJ01kBBqMiZU6U/mVCdJArbzBBupx9e1DCTIsu21csclkki6OzTADJ34hfNzEGishU qdsSJyr0z6l6U91QPt8AFjTambn5tWIU7kRSVe98= Date: Wed, 2 Oct 2024 14:08:24 -0700 From: Andrew Morton To: Frederic Weisbecker Cc: Thomas Gleixner , LKML , Hillf Danton , Tejun Heo , syzbot+943d34fa3cf2191e3068@syzkaller.appspotmail.com Subject: Re: [PATCH] kthread: Unpark only parked kthread Message-Id: <20241002140824.0a3ccc8695f16958f28c6d6c@linux-foundation.org> In-Reply-To: References: <20240913214634.12557-1-frederic@kernel.org> <20240926132130.b1d1f6943d225368d3062d5e@linux-foundation.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On Wed, 2 Oct 2024 16:15:05 +0200 Frederic Weisbecker = wrote: > Le Thu, Sep 26, 2024 at 01:21:30PM -0700, Andrew Morton a =E9crit : > > On Fri, 13 Sep 2024 23:46:34 +0200 Frederic Weisbecker wrote: > >=20 > > > Calling into kthread unparking unconditionally is mostly harmless when > > > the kthread is already unparked. The wake up is then simply ignored > > > because the target is not in TASK_PARKED state. > > >=20 > > > However if the kthread is per CPU, the wake up is preceded by a call > > > to kthread_bind() which expects the task to be inactive and in > > > TASK_PARKED state, which obviously isn't the case if it is unparked. > > >=20 > > > As a result, calling kthread_stop() on an unparked per-cpu kthread > > > triggers such a warning: > > >=20 > > > WARNING: CPU: 0 PID: 11 at kernel/kthread.c:525 __kthread_bind_mask = kernel/kthread.c:525 > > > > > > kthread_stop+0x17a/0x630 kernel/kthread.c:707 > > > destroy_workqueue+0x136/0xc40 kernel/workqueue.c:5810 > > > wg_destruct+0x1e2/0x2e0 drivers/net/wireguard/device.c:257 > > > netdev_run_todo+0xe1a/0x1000 net/core/dev.c:10693 > > > default_device_exit_batch+0xa14/0xa90 net/core/dev.c:11769 > > > ops_exit_list net/core/net_namespace.c:178 [inline] > > > cleanup_net+0x89d/0xcc0 net/core/net_namespace.c:640 > > > process_one_work kernel/workqueue.c:3231 [inline] > > > process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312 > > > worker_thread+0x86d/0xd70 kernel/workqueue.c:3393 > > > kthread+0x2f0/0x390 kernel/kthread.c:389 > > > ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 > > > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 > > > > > >=20 > > > Fix this with skipping unecessary unparking while stopping a kthread. > >=20 > > How does userspace trigger this? Is it an issue in current mainline? >=20 > I guess it takes some module unload performing a destroy workqueue to > trigger this. And it's an issue in current mainline. Cool. > >=20 > > Should we backport the fix into -stable kernels (depends on the answers > > to the above questions). > >=20 > > It looks like the issue is old, so a Fixes: probably isn't needed. But > > as the issue is old, why did it come to light now? >=20 > It's hard to tell. The core of the issue is there for a long while but > the conditions for it to really happen in practice is probably since: >=20 > 5c25b5ff89f0 (workqueue: Tag bound workers with KTHREAD_IS_PER_CPU) >=20 > So it might deserve a Fixes: actually. OK, thsnks I added Fixes: 5c25b5ff89f0 ("workqueue: Tag bound workers with KTHREAD_IS_PER_CPU") Cc: and it's queued for a 6.12-rcX merge.