linux-kernel - [PATCH] soc: xilinx: Fix for call trace due to the usage of smp_processor

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Message-ID: <20231027055622.21544-1-jay.buddhabhatti@amd.com>
Date:   Thu, 26 Oct 2023 22:56:22 -0700
From:   Jay Buddhabhatti <jay.buddhabhatti@....com>
To:     <michal.simek@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] soc: xilinx: Fix for call trace due to the usage of smp_processor_id()

From: HariBabu Gattem <haribabu.gattem@...inx.com>

When preemption is enabled in kernel and if any task which can be
preempted should not use smp_processor_id() directly, since CPU
switch can happen at any time, the previous value of cpu_id
differs with current cpu_id. As a result we see the below call trace
during xlnx_event_manager_probe.

[ 6.140197] dump_backtrace+0x0/0x190
[ 6.143884] show_stack+0x18/0x40
[ 6.147220] dump_stack_lvl+0x7c/0xa0
[ 6.150907] dump_stack+0x18/0x34
[ 6.154241] check_preemption_disabled+0x124/0x134
[ 6.159068] debug_smp_processor_id+0x20/0x2c
[ 6.163453] xlnx_event_manager_probe+0x48/0x250

To protect cpu_id, It is recommended to use get_cpu()/put_cpu()
to disable preemption, get the cpu_id and enable preemption respectively.
(For Reference, Documentation/locking/preempt-locking.rst and
Documentation/kernel-hacking/hacking.rst)

Use preempt_disable()/smp_processor_id()/preempt_enable()
API's to achieve the same.

Signed-off-by: HariBabu Gattem <haribabu.gattem@...inx.com>
Signed-off-by: Jay Buddhabhatti <jay.buddhabhatti@....com>
---
 drivers/soc/xilinx/xlnx_event_manager.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/soc/xilinx/xlnx_event_manager.c b/drivers/soc/xilinx/xlnx_event_manager.c
index 86a048a10a13..edfb1d5c10c6 100644
--- a/drivers/soc/xilinx/xlnx_event_manager.c
+++ b/drivers/soc/xilinx/xlnx_event_manager.c
@@ -555,7 +555,7 @@ static void xlnx_disable_percpu_irq(void *data)
 static int xlnx_event_init_sgi(struct platform_device *pdev)
 {
 	int ret = 0;
-	int cpu = smp_processor_id();
+	int cpu;
 	/*
 	 * IRQ related structures are used for the following:
 	 * for each SGI interrupt ensure its mapped by GIC IRQ domain
@@ -592,9 +592,12 @@ static int xlnx_event_init_sgi(struct platform_device *pdev)
 	sgi_fwspec.param[0] = sgi_num;
 	virq_sgi = irq_create_fwspec_mapping(&sgi_fwspec);
 
+	cpu = get_cpu();
 	per_cpu(cpu_number1, cpu) = cpu;
 	ret = request_percpu_irq(virq_sgi, xlnx_event_handler, "xlnx_event_mgmt",
 				 &cpu_number1);
+	put_cpu();
+
 	WARN_ON(ret);
 	if (ret) {
 		irq_dispose_mapping(virq_sgi);
-- 
2.17.1