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

Ryo Takakura
2024-12-18T12:00:47Z

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>
---

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