Messages in this thread | | | Subject | Re: [PATCH] coresight: trbe: Defer the probe on offline CPUs | From | Suzuki K Poulose <> | Date | Thu, 14 Oct 2021 13:39:17 +0100 |
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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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