Re: [PATCH] coresight: trbe: Defer the probe on offline CPUs

[Anshuman Khandual]

Hi Suzuki,

On 10/13/21 10:03 PM, Suzuki K Poulose wrote:
> 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.

Which pointer deference fails here exactly ?

static void arm_trbe_register_coresight_cpu(struct trbe_drvdata *drvdata, int cpu)
{
        struct trbe_cpudata *cpudata = per_cpu_ptr(drvdata->cpudata, cpu);
        struct coresight_device *trbe_csdev = coresight_get_percpu_sink(cpu);
        struct coresight_desc desc = { 0 };
        struct device *dev;

        if (WARN_ON(trbe_csdev))
                return;

        dev = &cpudata->drvdata->pdev->dev;   <---- Fails here

cpudata->drvdata link gets established in arm_trbe_probe_cpu() which
would not have run on an offline cpu.

> 
> e.g:

Should probably also mention the exact point of dereference failure
before this error message here.

> 
> [    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.
> 
> Fixes: 3fbf7f011f24 ("coresight: sink: Add TRBE driver")
> Reported-by: Bransilav Rankov <branislav.rankov@xxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> Tested-by: Branislav Rankov <branislav.rankov@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
>  drivers/hwtracing/coresight/coresight-trbe.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 5d350acef798..85ceda68af82 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -1286,7 +1286,9 @@ 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))
> 

Right, LGTM. Although I guess the following addition might be worthwhile
just to highlight the fact that cpudata->drvdata is not valid unless the
cpu has gone through arm_trbe_probe_cpu() first.

--- a/drivers/hwtracing/coresight/coresight-trbe.c
+++ b/drivers/hwtracing/coresight/coresight-trbe.c
@@ -869,6 +869,7 @@ static void arm_trbe_register_coresight_cpu(struct trbe_drvdata *drvdata, int cp
        if (WARN_ON(trbe_csdev))
                return;
 
+       WARN_ON(!cpudata->drvdata);
        dev = &cpudata->drvdata->pdev->dev;
        desc.name = devm_kasprintf(dev, GFP_KERNEL, "trbe%d", cpu);
        if (!desc.name)