[PATCH v2] PCI: endpoint: pci-epf-test: Fix sleeping function being called from atomic context

[Bhanu Seshu Kumar Valluri <bhanuseshukumar@gmail.com>]

When Root Complex(RC) triggers a Doorbell MSI interrupt to Endpoint(EP) it triggers a warning
in the EP. pci_endpoint kselftest target is compiled and used to run the Doorbell test in RC.

[  474.686193] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:271
[  474.710934] Call trace:
[  474.710995]  __might_resched+0x130/0x158
[  474.711011]  __might_sleep+0x70/0x88
[  474.711023]  mutex_lock+0x2c/0x80
[  474.711036]  pci_epc_get_msi+0x78/0xd8
[  474.711052]  pci_epf_test_raise_irq.isra.0+0x74/0x138
[  474.711063]  pci_epf_test_doorbell_handler+0x34/0x50

The BUG arises because the EP's pci_epf_test_doorbell_handler is making an
indirect call to pci_epc_get_msi, which uses mutex inside, from interrupt context.

To fix the issue convert hard irq handler to a threaded irq handler to allow it
to call functions that can sleep during bottom half execution. Register threaded
irq handler with IRQF_ONESHOT to keep interrupt line disabled until the threaded
irq handler completes execution.

Fixes: eff0c286aa91 ("PCI: endpoint: pci-epf-test: Add doorbell test support")
Signed-off-by: Bhanu Seshu Kumar Valluri <bhanuseshukumar@gmail.com>
---
 Note : It is compiled and tested on TI am642 board.

 Change log. V1->V2: 
  Trimmed Call trace to include only essential calls.
  Used 12 digit commit ID in fixes tag.
  Steps to reproduce the bug are removed from commit log.
  Link to V1: https://lore.kernel.org/all/20250917161817.15776-1-bhanuseshukumar@gmail.com/
 	
 Warnings can be reproduced by following steps below.
 *On EP side:
 1. Configure the pci-epf-test function using steps given below
   mount -t configfs none /sys/kernel/config
   cd /sys/kernel/config/pci_ep/
   mkdir functions/pci_epf_test/func1
   echo 0x104c > functions/pci_epf_test/func1/vendorid
   echo 0xb010 > functions/pci_epf_test/func1/deviceid
   echo 32 > functions/pci_epf_test/func1/msi_interrupts
   echo 2048 > functions/pci_epf_test/func1/msix_interrupts
   ln -s functions/pci_epf_test/func1 controllers/f102000.pcie-ep/
   echo 1 > controllers/f102000.pcie-ep/start

 *On RC side:
 1. Once EP side configuration is done do pci rescan.
   echo 1 > /sys/bus/pci/rescan
 2. Run Doorbell MSI test using pci_endpoint_test kselftest app.
  ./pci_endpoint_test -r pcie_ep_doorbell.DOORBELL_TEST
  Note: Kernel is compiled with CONFIG_DEBUG_KERNEL enabled.

 drivers/pci/endpoint/functions/pci-epf-test.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
index e091193bd8a8..c9e2eb930ad3 100644
--- a/drivers/pci/endpoint/functions/pci-epf-test.c
+++ b/drivers/pci/endpoint/functions/pci-epf-test.c
@@ -725,8 +725,8 @@ static void pci_epf_test_enable_doorbell(struct pci_epf_test *epf_test,
 	if (bar < BAR_0)
 		goto err_doorbell_cleanup;
 
-	ret = request_irq(epf->db_msg[0].virq, pci_epf_test_doorbell_handler, 0,
-			  "pci-ep-test-doorbell", epf_test);
+	ret = request_threaded_irq(epf->db_msg[0].virq, NULL, pci_epf_test_doorbell_handler,
+				   IRQF_ONESHOT, "pci-ep-test-doorbell", epf_test);
 	if (ret) {
 		dev_err(&epf->dev,
 			"Failed to request doorbell IRQ: %d\n",
-- 
2.34.1