Re: [PATCH v2] PCI: vmd: Fix spinlock usage on config access for RT kernel

["Luis Claudio R. Goncalves" <lgoncalv@redhat.com>]

On Wed, Dec 18, 2024 at 08:59:51PM +0900, Ryo Takakura wrote:
> PCI config access is locked with pci_lock which serializes
> pci_user/bus_write_config*() and pci_user/bus_read_config*().
> The subsequently invoked vmd_pci_write() and vmd_pci_read() are also
> serialized as they are only invoked by them respectively.
> 
> Remove cfg_lock which is taken by vmd_pci_write() and vmd_pci_read()
> for their serialization as its already serialized by pci_lock.
> 
> This fixes the spinlock_t(cfg_lock) usage within
> raw_spinlock_t(pci_lock) on RT kernels where spinlock_t becomes
> sleepable.
> 
> Reported as following:
> [   18.756807] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
> [   18.756810] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1617, name: nodedev-init
> [   18.756810] preempt_count: 1, expected: 0
> [   18.756811] RCU nest depth: 0, expected: 0
> [   18.756811] INFO: lockdep is turned off.
> [   18.756812] irq event stamp: 0
> [   18.756812] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
> [   18.756815] hardirqs last disabled at (0): [<ffffffff864f1fe2>] copy_process+0xa62/0x2d90
> [   18.756819] softirqs last  enabled at (0): [<ffffffff864f1fe2>] copy_process+0xa62/0x2d90
> [   18.756820] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [   18.756822] CPU: 3 UID: 0 PID: 1617 Comm: nodedev-init Tainted: G        W          6.12.1 #11
> [   18.756823] Tainted: [W]=WARN
> [   18.756824] Hardware name: Dell Inc. Vostro 3710/0K1D6X, BIOS 1.14.0 06/09/2023
> [   18.756825] Call Trace:
> [   18.756826]  <TASK>
> [   18.756827]  dump_stack_lvl+0x9b/0xf0
> [   18.756830]  dump_stack+0x10/0x20
> [   18.756831]  __might_resched+0x158/0x230
> [   18.756833]  rt_spin_lock+0x4e/0x130
> [   18.756837]  ? vmd_pci_read+0x8d/0x100 [vmd]
> [   18.756839]  vmd_pci_read+0x8d/0x100 [vmd]
> [   18.756840]  pci_user_read_config_byte+0x6f/0xe0
> [   18.756843]  pci_read_config+0xfe/0x290
> [   18.756845]  sysfs_kf_bin_read+0x68/0x90
> [   18.756847]  kernfs_fop_read_iter+0xd7/0x200
> [   18.756850]  vfs_read+0x26d/0x360
> [   18.756853]  ksys_read+0x70/0xf0
> [   18.756855]  __x64_sys_read+0x1a/0x20
> [   18.756857]  x64_sys_call+0x1715/0x20d0
> [   18.756859]  do_syscall_64+0x8f/0x170
> [   18.756861]  ? syscall_exit_to_user_mode+0xcd/0x2c0
> [   18.756863]  ? do_syscall_64+0x9b/0x170
> [   18.756865]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> 
> Signed-off-by: Ryo Takakura <ryotkkr98@gmail.com>
> ---

Reviewed-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>

Best regards,
Luis
 
> Thanks Luis for feedback!
> 
> Changes since v1:
> https://lore.kernel.org/lkml/20241215141321.383144-1-ryotkkr98@gmail.com/T/
> 
> - Remove cfg_lock instead of converting it to raw spinlock as suggested
>   by Sebastian[0].
>   
> [0] https://lore.kernel.org/linux-rt-users/20230620154434.MosrzRUh@linutronix.de/
> 
> ---
>  drivers/pci/controller/vmd.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 9d9596947..2be898424 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -125,7 +125,6 @@ struct vmd_irq_list {
>  struct vmd_dev {
>  	struct pci_dev		*dev;
>  
> -	spinlock_t		cfg_lock;
>  	void __iomem		*cfgbar;
>  
>  	int msix_count;
> @@ -385,13 +384,11 @@ static int vmd_pci_read(struct pci_bus *bus, unsigned int devfn, int reg,
>  {
>  	struct vmd_dev *vmd = vmd_from_bus(bus);
>  	void __iomem *addr = vmd_cfg_addr(vmd, bus, devfn, reg, len);
> -	unsigned long flags;
>  	int ret = 0;
>  
>  	if (!addr)
>  		return -EFAULT;
>  
> -	spin_lock_irqsave(&vmd->cfg_lock, flags);
>  	switch (len) {
>  	case 1:
>  		*value = readb(addr);
> @@ -406,7 +403,6 @@ static int vmd_pci_read(struct pci_bus *bus, unsigned int devfn, int reg,
>  		ret = -EINVAL;
>  		break;
>  	}
> -	spin_unlock_irqrestore(&vmd->cfg_lock, flags);
>  	return ret;
>  }
>  
> @@ -420,13 +416,11 @@ static int vmd_pci_write(struct pci_bus *bus, unsigned int devfn, int reg,
>  {
>  	struct vmd_dev *vmd = vmd_from_bus(bus);
>  	void __iomem *addr = vmd_cfg_addr(vmd, bus, devfn, reg, len);
> -	unsigned long flags;
>  	int ret = 0;
>  
>  	if (!addr)
>  		return -EFAULT;
>  
> -	spin_lock_irqsave(&vmd->cfg_lock, flags);
>  	switch (len) {
>  	case 1:
>  		writeb(value, addr);
> @@ -444,7 +438,6 @@ static int vmd_pci_write(struct pci_bus *bus, unsigned int devfn, int reg,
>  		ret = -EINVAL;
>  		break;
>  	}
> -	spin_unlock_irqrestore(&vmd->cfg_lock, flags);
>  	return ret;
>  }
>  
> @@ -1009,7 +1002,6 @@ 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);
>  	pci_set_drvdata(dev, vmd);
>  	err = vmd_enable_domain(vmd, features);
>  	if (err)
> -- 
> 2.34.1
> 
---end quoted text---