| Message ID | 20250218080830.ufw3IgyX@linutronix.de (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Krzysztof Wilczyński |
| Headers | show |
| Series | [v4] PCI: vmd: Make vmd_dev::cfg_lock a raw_spinlock_t. | expand |
Hello, > 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. > The vmd_dev::cfg_lock is accessed in the same context as the pci_lock. > > Make vmd_dev::cfg_lock a raw_spinlock_t. Applied to controller/vmd, thank you! Krzysztof
On Tue, Feb 18, 2025 at 09:08:30AM +0100, Sebastian Andrzej Siewior wrote: > From: Ryo Takakura <ryotkkr98@gmail.com> > > 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 <ryotkkr98@gmail.com> > Tested-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com> > Acked-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > --- > 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 >
Hello, > > 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. I changed the commit log directly on the relevant branch. Thank you! Krzysztof
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)