patch "coresight: trbe: Defer the probe on offline CPUs" added to char-misc-next

This is a note to let you know that I've just added the patch titled

coresight: trbe: Defer the probe on offline CPUs

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From a08025b3fe56185290a1ea476581f03ca733f967 Mon Sep 17 00:00:00 2001
From: Suzuki K Poulose <[email protected]>
Date: Thu, 14 Oct 2021 15:22:38 +0100
Subject: coresight: trbe: Defer the probe on offline CPUs

If a CPU is offline during the driver init, we could end up causing a kernel crash trying to register the coresight device for the TRBE instance. The trbe_cpudata for the TRBE instance is initialized only when it is probed. Otherwise, we could end up dereferencing a NULL cpudata->drvdata.

e.g:

[    0.149999] coresight ete0: CPU0: ete v1.1 initialized
[    0.149999] coresight-etm4x ete_1: ETM arch init failed
[    0.149999] coresight-etm4x: probe of ete_1 failed with error -22
[    0.150085] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000050
[    0.150085] Mem abort info:
[    0.150085]   ESR = 0x96000005
[    0.150085]   EC = 0x25: DABT (current EL), IL = 32 bits
[    0.150085]   SET = 0, FnV = 0
[    0.150085]   EA = 0, S1PTW = 0
[    0.150085] Data abort info:
[    0.150085]   ISV = 0, ISS = 0x00000005
[    0.150085]   CM = 0, WnR = 0
[    0.150085] [0000000000000050] user address but active_mm is swapper
[    0.150085] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[    0.150085] Modules linked in:
[    0.150085] Hardware name: FVP Base RevC (DT)
[    0.150085] pstate: 00800009 (nzcv daif -PAN +UAO -TCO BTYPE=--)
[    0.150155] pc : arm_trbe_register_coresight_cpu+0x74/0x144
[    0.150155] lr : arm_trbe_register_coresight_cpu+0x48/0x144
  ...

[    0.150237] Call trace:
[    0.150237]  arm_trbe_register_coresight_cpu+0x74/0x144
[    0.150237]  arm_trbe_device_probe+0x1c0/0x2d8
[    0.150259]  platform_drv_probe+0x94/0xbc
[    0.150259]  really_probe+0x1bc/0x4a8
[    0.150266]  driver_probe_device+0x7c/0xb8
[    0.150266]  device_driver_attach+0x6c/0xac
[    0.150266]  __driver_attach+0xc4/0x148
[    0.150266]  bus_for_each_dev+0x7c/0xc8
[    0.150266]  driver_attach+0x24/0x30
[    0.150266]  bus_add_driver+0x100/0x1e0
[    0.150266]  driver_register+0x78/0x110
[    0.150266]  __platform_driver_register+0x44/0x50
[    0.150266]  arm_trbe_init+0x28/0x84
[    0.150266]  do_one_initcall+0x94/0x2bc
[    0.150266]  do_initcall_level+0xa4/0x158
[    0.150266]  do_initcalls+0x54/0x94
[    0.150319]  do_basic_setup+0x24/0x30
[    0.150319]  kernel_init_freeable+0xe8/0x14c
[    0.150319]  kernel_init+0x14/0x18c
[    0.150319]  ret_from_fork+0x10/0x30
[    0.150319] Code: f94012c8 b0004ce2 9134a442 52819801 (f9402917)
[    0.150319] ---[ end trace d23e0cfe5098535e ]---
[    0.150346] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Fix this by skipping the step, if we are unable to probe the CPU.

---
 drivers/hwtracing/coresight/coresight-trbe.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

index 2825ccb0cf39..5d77baba8b0f 100644
@@ -893,6 +893,10 @@ static void arm_trbe_register_coresight_cpu(struct trbe_drvdata *drvdata, int cp
 	if (WARN_ON(trbe_csdev))
 		return;
 
+	/* If the TRBE was not probed on the CPU, we shouldn't be here */
+	if (WARN_ON(!cpudata->drvdata))
+		return;
+
 	dev = &cpudata->drvdata->pdev->dev;
 	desc.name = devm_kasprintf(dev, GFP_KERNEL, "trbe%d", cpu);
 	if (!desc.name)

@@ -974,7 +978,9 @@ static int arm_trbe_probe_coresight(struct trbe_drvdata *drvdata)
 		return -ENOMEM;
 
 	for_each_cpu(cpu, &drvdata->supported_cpus) {
-		smp_call_function_single(cpu, arm_trbe_probe_cpu, drvdata, 1);
+		/* If we fail to probe the CPU, let us defer it to hotplug callbacks */
+		if (smp_call_function_single(cpu, arm_trbe_probe_cpu, drvdata, 1))
+			continue;
 		if (cpumask_test_cpu(cpu, &drvdata->supported_cpus))
 			arm_trbe_register_coresight_cpu(drvdata, cpu);
 		if (cpumask_test_cpu(cpu, &drvdata->supported_cpus))

2.33.1