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Message-ID: <20240619200039.GA1319210@bhelgaas>
Date: Wed, 19 Jun 2024 15:00:39 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Jiwei Sun <sunjw10@...look.com>
Cc: nirmal.patel@...ux.intel.com, jonathan.derrick@...ux.dev,
lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org,
bhelgaas@...gle.com, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, sunjw10@...ovo.com,
ahuang12@...ovo.com, Thomas Gleixner <tglx@...utronix.de>,
Keith Busch <kbusch@...nel.org>
Subject: Re: [PATCH] PCI: vmd: Use raw spinlock for cfg_lock
[+cc Thomas in case he has msi_lock comment, Keith in case he has
cfg_lock comment]
On Wed, Jun 19, 2024 at 07:27:59PM +0800, Jiwei Sun wrote:
> From: Jiwei Sun <sunjw10@...ovo.com>
>
> If the kernel is built with the following configurations and booting
> CONFIG_VMD=y
> CONFIG_DEBUG_LOCKDEP=y
> CONFIG_DEBUG_SPINLOCK=y
> CONFIG_PROVE_LOCKING=y
> CONFIG_PROVE_RAW_LOCK_NESTING=y
>
> The following log appears,
>
> =============================
> [ BUG: Invalid wait context ]
> 6.10.0-rc4 #80 Not tainted
> -----------------------------
> kworker/18:2/633 is trying to lock:
> ffff888c474e5648 (&vmd->cfg_lock){....}-{3:3}, at: vmd_pci_write+0x185/0x2a0
> other info that might help us debug this:
> context-{5:5}
> 4 locks held by kworker/18:2/633:
> #0: ffff888100108958 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0xf78/0x1920
> #1: ffffc9000ae1fd90 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: process_one_work+0x7fe/0x1920
> #2: ffff888c483508a8 (&md->mutex){+.+.}-{4:4}, at: __pci_enable_msi_range+0x208/0x800
> #3: ffff888c48329bd8 (&dev->msi_lock){....}-{2:2}, at: pci_msi_update_mask+0x91/0x170
> stack backtrace:
> CPU: 18 PID: 633 Comm: kworker/18:2 Not tainted 6.10.0-rc4 #80 7c0f2526417bfbb7579e3c3442683c5961773c75
> Hardware name: Lenovo ThinkSystem SR630/-[7X01RCZ000]-, BIOS IVEL60O-2.71 09/28/2020
> Workqueue: events work_for_cpu_fn
> Call Trace:
> <TASK>
> dump_stack_lvl+0x7c/0xc0
> __lock_acquire+0x9e5/0x1ed0
> lock_acquire+0x194/0x490
> _raw_spin_lock_irqsave+0x42/0x90
> vmd_pci_write+0x185/0x2a0
> pci_msi_update_mask+0x10c/0x170
> __pci_enable_msi_range+0x291/0x800
> pci_alloc_irq_vectors_affinity+0x13e/0x1d0
> pcie_portdrv_probe+0x570/0xe60
> local_pci_probe+0xdc/0x190
> work_for_cpu_fn+0x4e/0xa0
> process_one_work+0x86d/0x1920
> process_scheduled_works+0xd7/0x140
> worker_thread+0x3e9/0xb90
> kthread+0x2e9/0x3d0
> ret_from_fork+0x2d/0x60
> ret_from_fork_asm+0x1a/0x30
> </TASK>
>
> The root cause is that the dev->msi_lock is a raw spinlock, but
> vmd->cfg_lock is a spinlock.
Can you expand this a little bit? This isn't enough unless one
already knows the difference between raw_spinlock_t and spinlock_t,
which I didn't.
Documentation/locking/locktypes.rst says they are the same except when
CONFIG_PREEMPT_RT is set (might be worth mentioning with the config
list above?), but that with CONFIG_PREEMPT_RT, spinlock_t is based on
rt_mutex.
And I guess there's a rule that you can't acquire rt_mutex while
holding a raw_spinlock.
The dev->msi_lock was added by 77e89afc25f3 ("PCI/MSI: Protect
msi_desc::masked for multi-MSI") and only used in
pci_msi_update_mask():
raw_spin_lock_irqsave(lock, flags);
desc->pci.msi_mask &= ~clear;
desc->pci.msi_mask |= set;
pci_write_config_dword(msi_desc_to_pci_dev(desc), desc->pci.mask_pos,
desc->pci.msi_mask);
raw_spin_unlock_irqrestore(lock, flags);
The vmd->cfg_lock was added by 185a383ada2e ("x86/PCI: Add driver for
Intel Volume Management Device (VMD)") and is only used around VMD
config accesses, e.g.,
* CPU may deadlock if config space is not serialized on some versions of this
* hardware, so all config space access is done under a spinlock.
static int vmd_pci_read(...)
{
spin_lock_irqsave(&vmd->cfg_lock, flags);
switch (len) {
case 1:
*value = readb(addr);
break;
case 2:
*value = readw(addr);
break;
case 4:
*value = readl(addr);
break;
default:
ret = -EINVAL;
break;
}
spin_unlock_irqrestore(&vmd->cfg_lock, flags);
}
IIUC those reads turn into single PCIe MMIO reads, so I wouldn't
expect any concurrency issues there that need locking.
But apparently there's something weird that can deadlock the CPU.
> Signed-off-by: Jiwei Sun<sunjw10@...ovo.com>
> Suggested-by: Adrian Huang <ahuang12@...ovo.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 87b7856f375a..45d0ebf96adc 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;
> @@ -402,7 +402,7 @@ 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);
> @@ -417,7 +417,7 @@ 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;
> }
>
> @@ -437,7 +437,7 @@ 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);
> @@ -455,7 +455,7 @@ 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;
> }
>
> @@ -1015,7 +1015,7 @@ 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)
> --
> 2.27.0
>
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