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SubjectRe: [PATCH] coresight: trbe: Defer the probe on offline CPUs
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On 14/10/2021 04:28, Anshuman Khandual wrote:
> 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.

Yes, that is correct.

>
>>
>> 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@arm.com>
>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
>> Cc: Mike Leach <mike.leach@linaro.org>
>> Cc: Leo Yan <leo.yan@linaro.org>
>> Tested-by: Branislav Rankov <branislav.rankov@arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>> 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);

Ok, I would rather return here with the warning. I will send
a revision.

Thanks !

Suzuki

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