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Date: Thu, 14 Oct 2021 08:58:54 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>,
mathieu.poirier@...aro.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
coresight@...ts.linaro.org,
Bransilav Rankov <branislav.rankov@....com>,
Mike Leach <mike.leach@...aro.org>,
Leo Yan <leo.yan@...aro.org>
Subject: Re: [PATCH] coresight: trbe: Defer the probe on offline CPUs
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@....com>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Leo Yan <leo.yan@...aro.org>
> Tested-by: Branislav Rankov <branislav.rankov@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....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);
dev = &cpudata->drvdata->pdev->dev;
desc.name = devm_kasprintf(dev, GFP_KERNEL, "trbe%d", cpu);
if (!desc.name)
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