ntb_epf_vec_isr() calls pci_irq_vector() in hardirq context to derive
the vector number. pci_irq_vector() calls msi_get_virq() that takes a
mutex and can therefore trigger "scheduling while atomic" splats.

  BUG: scheduling while atomic: kworker/u33:0/55/0x00010001
  ...
  Call trace:
   ...
   schedule+0x38/0x110
   schedule_preempt_disabled+0x28/0x50
   __mutex_lock.constprop.0+0x848/0x908
   __mutex_lock_slowpath+0x18/0x30
   mutex_lock+0x4c/0x60
   msi_domain_get_virq+0xe8/0x138
   pci_irq_vector+0x2c/0x60
   ntb_epf_vec_isr+0x28/0x120 [ntb_hw_epf]
   __handle_irq_event_percpu+0x70/0x3a8
   handle_irq_event+0x48/0x100
   handle_edge_irq+0x100/0x1c8
   ...

Cache the Linux IRQ number for vector 0 when vectors are allocated and
use it as a base in the ISR. Running the ISR in a threaded IRQ handler
would also avoid the problem, but that would be unnecessary here.

Cc: stable@vger.kernel.org # v5.12+
Fixes: 812ce2f8d14e ("NTB: Add support for EPF PCI Non-Transparent Bridge")
Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
 drivers/ntb/hw/epf/ntb_hw_epf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
index 5a35f341f821..8925c688930c 100644
--- a/drivers/ntb/hw/epf/ntb_hw_epf.c
+++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
@@ -92,6 +92,7 @@ struct ntb_epf_dev {
 
 	int db_val;
 	u64 db_valid_mask;
+	int irq_base;
 };
 
 #define ntb_ndev(__ntb) container_of(__ntb, struct ntb_epf_dev, ntb)
@@ -318,7 +319,7 @@ static irqreturn_t ntb_epf_vec_isr(int irq, void *dev)
 	struct ntb_epf_dev *ndev = dev;
 	int irq_no;
 
-	irq_no = irq - pci_irq_vector(ndev->ntb.pdev, 0);
+	irq_no = irq - ndev->irq_base;
 	ndev->db_val = irq_no + 1;
 
 	if (irq_no == 0)
@@ -350,6 +351,7 @@ static int ntb_epf_init_isr(struct ntb_epf_dev *ndev, int msi_min, int msi_max)
 		argument &= ~MSIX_ENABLE;
 	}
 
+	ndev->irq_base = pci_irq_vector(pdev, 0);
 	for (i = 0; i < irq; i++) {
 		ret = request_irq(pci_irq_vector(pdev, i), ntb_epf_vec_isr,
 				  0, "ntb_epf", ndev);
-- 
2.51.0