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 2529B265635; Thu, 20 Feb 2025 22:59:50 +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=1740092391; cv=none; b=vF0WY+obiBFt8/jbk8JzU2ysDYuYCdUgP3kNLhVC7BRAXh2JWAPg0et/1uzib1KNRape8FJO3jRrU5Zd8QpPY2uw8v88RsK1QwKtOn1LRh1X7fMTcFICFfV2WIr40GTsjuErPrJzeZiNnOWIO4LUl59p1qDtTb4zTmJVELZbHbA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740092391; c=relaxed/simple; bh=3S+TCq9Fx8ACf/yVx79pjGFNRic4JKbeNZIjQEJfLqA=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=KW/ffsdjhzX2+cZo993Tgwf/wR0R8wE8/xVg7vK0MLfyVSQ27qju5OtiqvgCddWAn5R++FD7ALhj2ERC9Wx12yngxGVIVsyRK0N0+yDZY1ufUFIVelg3r9ZvuIA3KdSpDVP6Mrvse5u7MMLKLDeqvhod/Nr0iCExaUxgNGc6ELc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=g2iTOlc8; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="g2iTOlc8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 732FAC4CED1; Thu, 20 Feb 2025 22:59:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740092390; bh=3S+TCq9Fx8ACf/yVx79pjGFNRic4JKbeNZIjQEJfLqA=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=g2iTOlc8adtYCkf1+qhUD/uYV0fpGwPYOjAx3hyOYjjGrVwAPYZpWFgZzgS4Q3FSa dzIs3ecCv/1IA1mMkKHHWdabeEd1R5DX6SVwuccVrUthK0+g8ZPaIKlcKfNEp96dG4 imUaah3p4TyAFFBVrXjcgw+PgzpeYJzxByDFj5WczTSIkNKqHu6qQt3ycYeMkz2gem whsD4yTnIEqCOs/I+n2QC0UqwH79Q38cerLhdjfWzHygvx66OYzBlwB2hi0fGTDGd2 Pyq+uq6IWv7Qm/NJFlFswkyfKY7N8ImT90T6ackUhRZtVDKq9d2ZfMpbG8JOiHN5Gx RpHVIbfPVxS9g== Date: Thu, 20 Feb 2025 16:59:48 -0600 From: Bjorn Helgaas To: Sebastian Andrzej Siewior Cc: linux-pci@vger.kernel.org, "Luis Claudio R. Goncalves" , Ryo Takakura , bhelgaas@google.com, jonathan.derrick@linux.dev, kw@linux.com, lpieralisi@kernel.org, manivannan.sadhasivam@linaro.org, nirmal.patel@linux.intel.com, robh@kernel.org, rostedt@goodmis.org, kbusch@kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: Re: [PATCH v4] PCI: vmd: Make vmd_dev::cfg_lock a raw_spinlock_t. Message-ID: <20250220225948.GA318342@bhelgaas> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250218080830.ufw3IgyX@linutronix.de> On Tue, Feb 18, 2025 at 09:08:30AM +0100, Sebastian Andrzej Siewior wrote: > From: Ryo Takakura > > The access to the PCI config space via pci_ops::read and pci_ops::write > is a low-level hardware access. The functions can be accessed with > disabled interrupts even on PREEMPT_RT. The pci_lock has been made a > raw_spinlock_t for this purpose. A spinlock_t becomes a sleeping lock on > PREEMPT_RT can not be acquired with disabled interrupts. I think this is missing a word or two and should say: A spinlock_t becomes a sleeping lock on PREEMPT_RT, so it cannot be acquired with disabled interrupts. pci_ops.read() is called while holding the non-sleepable raw_spinlock_t pci_lock, so pci_ops.read() must also be non-sleepable. It's not really relevant that "pci_ops.read() can be called with disabled interrupts even on PREEMPT_RT". It can *always* be called with interrupts disabled. > The vmd_dev::cfg_lock is accessed in the same context as the pci_lock. > > Make vmd_dev::cfg_lock a raw_spinlock_t. > > [bigeasy: Reword commit message.] > > Signed-off-by: Ryo Takakura > Tested-by: Luis Claudio R. Goncalves > Acked-by: Luis Claudio R. Goncalves > Signed-off-by: Sebastian Andrzej Siewior > --- > Changes since v3 https://lore.kernel.org/all/20241219014549.24427-1-ryotkkr98@gmail.com/ > - Repost with updated changelog. > > Changes since v2 https://lore.kernel.org/lkml/20241218115951.83062-1-ryotkkr98@gmail.com/ > - In case if CONFIG_PCI_LOCKLESS_CONFIG is set, vmd_pci_read/write() > still neeed cfg_lock for their serialization. So instead of removing > it, convert it to raw spinlock. > > v1: https://lore.kernel.org/lkml/20241215141321.383144-1-ryotkkr98@gmail.com/ > > drivers/pci/controller/vmd.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c > index 9d9596947350f..94ceec50a2b94 100644 > --- a/drivers/pci/controller/vmd.c > +++ b/drivers/pci/controller/vmd.c > @@ -125,7 +125,7 @@ struct vmd_irq_list { > struct vmd_dev { > struct pci_dev *dev; > > - spinlock_t cfg_lock; > + raw_spinlock_t cfg_lock; > void __iomem *cfgbar; > > int msix_count; > @@ -391,7 +391,7 @@ static int vmd_pci_read(struct pci_bus *bus, unsigned int devfn, int reg, > if (!addr) > return -EFAULT; > > - spin_lock_irqsave(&vmd->cfg_lock, flags); > + raw_spin_lock_irqsave(&vmd->cfg_lock, flags); > switch (len) { > case 1: > *value = readb(addr); > @@ -406,7 +406,7 @@ static int vmd_pci_read(struct pci_bus *bus, unsigned int devfn, int reg, > ret = -EINVAL; > break; > } > - spin_unlock_irqrestore(&vmd->cfg_lock, flags); > + raw_spin_unlock_irqrestore(&vmd->cfg_lock, flags); > return ret; > } > > @@ -426,7 +426,7 @@ static int vmd_pci_write(struct pci_bus *bus, unsigned int devfn, int reg, > if (!addr) > return -EFAULT; > > - spin_lock_irqsave(&vmd->cfg_lock, flags); > + raw_spin_lock_irqsave(&vmd->cfg_lock, flags); > switch (len) { > case 1: > writeb(value, addr); > @@ -444,7 +444,7 @@ static int vmd_pci_write(struct pci_bus *bus, unsigned int devfn, int reg, > ret = -EINVAL; > break; > } > - spin_unlock_irqrestore(&vmd->cfg_lock, flags); > + raw_spin_unlock_irqrestore(&vmd->cfg_lock, flags); > return ret; > } > > @@ -1009,7 +1009,7 @@ static int vmd_probe(struct pci_dev *dev, const struct pci_device_id *id) > if (features & VMD_FEAT_OFFSET_FIRST_VECTOR) > vmd->first_vec = 1; > > - spin_lock_init(&vmd->cfg_lock); > + raw_spin_lock_init(&vmd->cfg_lock); > pci_set_drvdata(dev, vmd); > err = vmd_enable_domain(vmd, features); > if (err) > -- > 2.47.2 >