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

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Message-Id: <20250917161817.15776-1-bhanuseshukumar@gmail.com>
Date: Wed, 17 Sep 2025 21:48:17 +0530
From: Bhanu Seshu Kumar Valluri <bhanuseshukumar@...il.com>
To: Manivannan Sadhasivam <mani@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Petr Mladek <pmladek@...e.com>,
	Tejun Heo <tj@...nel.org>,
	Miri Korenblit <miriam.rachel.korenblit@...el.com>,
	Bhanu Seshu Kumar Valluri <bhanuseshukumar@...il.com>,
	Frank Li <Frank.Li@....com>
Cc: linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev,
	skhan@...uxfoundation.org
Subject: [PATCH] PCI: endpoint: pci-epf-test: Fix sleeping function being called from atomic context

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
[  474.694656] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 0, name: swapper/0
[  474.702473] preempt_count: 10001, expected: 0
[  474.706819] RCU nest depth: 0, expected: 0
[  474.710913] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.17.0-rc5-g7aac71907bde #12 PREEMPT
[  474.710926] Hardware name: Texas Instruments AM642 EVM (DT)
[  474.710934] Call trace:
[  474.710940]  show_stack+0x20/0x38 (C)
[  474.710969]  dump_stack_lvl+0x70/0x88
[  474.710984]  dump_stack+0x18/0x28
[  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
[  474.711072]  __handle_irq_event_percpu+0xac/0x1f0
[  474.711086]  handle_irq_event+0x54/0xb8
[  474.711096]  handle_fasteoi_irq+0x150/0x220
[  474.711110]  handle_irq_desc+0x48/0x68
[  474.711121]  generic_handle_domain_irq+0x24/0x38
[  474.711131]  gic_handle_irq+0x4c/0xc8
[  474.711141]  call_on_irq_stack+0x30/0x70
[  474.711151]  do_interrupt_handler+0x70/0x98
[  474.711163]  el1_interrupt+0x34/0x68
[  474.711176]  el1h_64_irq_handler+0x18/0x28
[  474.711189]  el1h_64_irq+0x6c/0x70
[  474.711198]  default_idle_call+0x10c/0x120 (P)
[  474.711208]  do_idle+0x128/0x268
[  474.711220]  cpu_startup_entry+0x3c/0x48
[  474.711231]  rest_init+0xe0/0xe8
[  474.711240]  start_kernel+0x6d4/0x760
[  474.711255]  __primary_switched+0x88/0x98

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.

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

This patch converts hard irq handler to a threaded irq handler to allow it
to call functions that can sleep during bottom half execution. The threaded
irq handler is registered with IRQF_ONESHOT and keeps interrupt line disabled
until the threaded irq handler completes execution.

Fixes: eff0c286aa916221a69126 ("PCI: endpoint: pci-epf-test: Add doorbell test support")
Signed-off-by: Bhanu Seshu Kumar Valluri <bhanuseshukumar@...il.com>
---
 Note : It is compiled and tested on TI am642 board.

 drivers/pci/endpoint/functions/pci-epf-test.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
index e091193bd..b9c1ad931 100644
--- a/drivers/pci/endpoint/functions/pci-epf-test.c
+++ b/drivers/pci/endpoint/functions/pci-epf-test.c
@@ -680,7 +680,7 @@ static void pci_epf_test_raise_irq(struct pci_epf_test *epf_test,
 	}
 }
 
-static irqreturn_t pci_epf_test_doorbell_handler(int irq, void *data)
+static irqreturn_t pci_epf_test_doorbell_irq_thread(int irq, void *data)
 {
 	struct pci_epf_test *epf_test = data;
 	enum pci_barno test_reg_bar = epf_test->test_reg_bar;
@@ -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_irq_thread,
+				   IRQF_ONESHOT, "pci-ep-test-doorbell", epf_test);
 	if (ret) {
 		dev_err(&epf->dev,
 			"Failed to request doorbell IRQ: %d\n",
-- 
2.34.1