From nobody Sun Dec 14 21:34:14 2025 Received: from forwardcorp1d.mail.yandex.net (forwardcorp1d.mail.yandex.net [178.154.239.200]) (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 495DB2459CF for ; Wed, 15 Jan 2025 13:19:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=178.154.239.200 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736947175; cv=none; b=uS3Xk9nJMSCb6cx+EQ6btOBDpBHkHyjXFvbrnqerxuyFhrui1D6zqgdPa8BMwAF4yIciQsVFfOgZLNGkeUCq4HxrwPAysnchv+5clr5yPHyuIUrnxR5JuU54uBC8W1W+NsBO0jxPbOHB8An28dZhzOpWuOJefR3OdRRjpgIB0rM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736947175; c=relaxed/simple; bh=Cw5TBSFk+TbXwuO0qcfOrMYH+pBWjwkl36xGStfa5XU=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=pyHrwgwpdbSXqyms05b9szwmaFPLj7Q81nAQQF1E+5pXNfwdoaGNMYyTchgwehf/htJr7biwNVj+A1rdD3HRIOWdjHUHByaPGjHwBj/VYhW5KulFr3EExnw2BGmDs9twsU9TTsPc4KdJYq6FxzgnoL1BfqYAs7sGMZwpanlDOQc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=yandex-team.ru; spf=pass smtp.mailfrom=yandex-team.ru; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b=dcPxTz62; arc=none smtp.client-ip=178.154.239.200 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=yandex-team.ru Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=yandex-team.ru Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="dcPxTz62" Received: from mail-nwsmtp-smtp-corp-main-56.klg.yp-c.yandex.net (mail-nwsmtp-smtp-corp-main-56.klg.yp-c.yandex.net [IPv6:2a02:6b8:c42:b1cb:0:640:2a1e:0]) by forwardcorp1d.mail.yandex.net (Yandex) with ESMTPS id 9FFF5609BF; Wed, 15 Jan 2025 16:17:45 +0300 (MSK) Received: from davydov-max-lin.yandex.net (unknown [2a02:6bf:8011:701:66e1:20a5:ba04:640b]) by mail-nwsmtp-smtp-corp-main-56.klg.yp-c.yandex.net (smtpcorp/Yandex) with ESMTPSA id XHQL1n0Ia4Y0-YMaBCLu5; Wed, 15 Jan 2025 16:17:44 +0300 X-Yandex-Fwd: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1736947064; bh=rlpJyeIT/aC8bk1n6SHPuEnqnDX1ITC4MnsD28zndAg=; h=Message-Id:Date:Cc:Subject:To:From; b=dcPxTz62tC8VWf/GtPDQVszWq7NU06iRiMkw/bMdsPaxK2mZBBZw33StWMcRcFG6O faRsktXAOW0z9MiYkQKIyGyRrzYUZaEznRYbA7FCwftZw39Cn+yHx/nWag5mlxRCn2 IvbPdVBvc5MUi0UWBdM6ahd5ZK7NAJKzGsFobmo4= Authentication-Results: mail-nwsmtp-smtp-corp-main-56.klg.yp-c.yandex.net; dkim=pass header.i=@yandex-team.ru From: Maksim Davydov To: linux-kernel@vger.kernel.org, x86@kernel.org Cc: davydov-max@yandex-team.ru, den-plotnikov@yandex-team.ru, gpiccoli@igalia.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com Subject: [PATCH RESEND v4] x86/split_lock: fix delayed detection enabling Date: Wed, 15 Jan 2025 16:17:04 +0300 Message-Id: <20250115131704.132609-1-davydov-max@yandex-team.ru> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" If the warn mode with disabled mitigation mode is used, then on each CPU where the split lock occurred detection will be disabled in order to make progress and delayed work will be scheduled, which then will enable detection back. Now it turns out that all CPUs use one global delayed work structure. This leads to the fact that if a split lock occurs on several CPUs at the same time (within 2 jiffies), only one CPU will schedule delayed work, but the rest will not. The return value of schedule_delayed_work_on() would have shown this, but it is not checked in the code. A diagram that can help to understand the bug reproduction: https://lore.kernel.org/all/2cd54041-253b-4e78-b8ea-dbe9b884ff9b@yandex-tea= m.ru/ In order to fix the warn mode with disabled mitigation mode, delayed work has to be a per-CPU. v4 -> v3: * rebased the patch onto the latest master v3 -> v2: * place and time of the per-CPU structure initialization were changed. initcall doesn't seem to be a good place for it, so deferred initialization is used. Fixes: 727209376f49 ("x86/split_lock: Add sysctl to control the misery mode= ") Signed-off-by: Maksim Davydov Tested-by: Guilherme G. Piccoli --- arch/x86/kernel/cpu/bus_lock.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/cpu/bus_lock.c b/arch/x86/kernel/cpu/bus_lock.c index 704e9241b964..b72235c8db3e 100644 --- a/arch/x86/kernel/cpu/bus_lock.c +++ b/arch/x86/kernel/cpu/bus_lock.c @@ -192,7 +192,13 @@ static void __split_lock_reenable(struct work_struct *= work) { sld_update_msr(true); } -static DECLARE_DELAYED_WORK(sl_reenable, __split_lock_reenable); +/* + * In order for each CPU to schedule itself delayed work independently of = the + * others, delayed work struct should be per-CPU. This is not required when + * sysctl_sld_mitigate is enabled because of the semaphore, that limits + * the number of simultaneously scheduled delayed works to 1. + */ +static DEFINE_PER_CPU(struct delayed_work, sl_reenable); =20 /* * If a CPU goes offline with pending delayed work to re-enable split lock @@ -213,7 +219,7 @@ static int splitlock_cpu_offline(unsigned int cpu) =20 static void split_lock_warn(unsigned long ip) { - struct delayed_work *work; + struct delayed_work *work =3D NULL; int cpu; =20 if (!current->reported_split_lock) @@ -235,11 +241,17 @@ static void split_lock_warn(unsigned long ip) if (down_interruptible(&buslock_sem) =3D=3D -EINTR) return; work =3D &sl_reenable_unlock; - } else { - work =3D &sl_reenable; } =20 cpu =3D get_cpu(); + + if (!work) { + work =3D this_cpu_ptr(&sl_reenable); + /* Deferred initialization of per-CPU struct */ + if (!work->work.func) + INIT_DELAYED_WORK(work, __split_lock_reenable); + } + schedule_delayed_work_on(cpu, work, 2); =20 /* Disable split lock detection on this CPU to make progress */ --=20 2.34.1