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perf/arm-cci: Remove broken race mitigation

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Uncore PMU drivers face an awkward cyclic dependency wherein:

 - They have to pick a valid online CPU to associate with before
   registering the PMU device, since it will get exposed to userspace
   immediately.
 - The PMU registration has to be be at least partly complete before
   hotplug events can be handled, since trying to migrate an
   uninitialised context would be bad.
 - The hotplug handler has to be ready as soon as a CPU is chosen, lest
   it go offline without the user-visible cpumask value getting updated.

The arm-cci driver has tried to solve this by using get_cpu() to pick
the current CPU and prevent it from disappearing while both
registrations are performed, but that results in taking mutexes with
preemption disabled, which makes certain configurations very unhappy:

[ 1.983337] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:2004
[ 1.983340] in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: swapper/0
[ 1.983342] Preemption disabled at:
[ 1.983353] [<ffffff80089801f4>] cci_pmu_probe+0x1dc/0x488
[ 1.983360] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.20-rt8-yocto-preempt-rt #1
[ 1.983362] Hardware name: ZynqMP ZCU102 Rev1.0 (DT)
[ 1.983364] Call trace:
[ 1.983369] dump_backtrace+0x0/0x158
[ 1.983372] show_stack+0x24/0x30
[ 1.983378] dump_stack+0x80/0xa4
[ 1.983383] ___might_sleep+0x138/0x160
[ 1.983386] __might_sleep+0x58/0x90
[ 1.983391] __rt_mutex_lock_state+0x30/0xc0
[ 1.983395] _mutex_lock+0x24/0x30
[ 1.983400] perf_pmu_register+0x2c/0x388
[ 1.983404] cci_pmu_probe+0x2bc/0x488
[ 1.983409] platform_drv_probe+0x58/0xa8

It is not feasible to resolve all the possible races outside of the perf
core itself, so address the immediate bug by following the example of
nearly every other PMU driver and not even trying to do so. Registering
the hotplug notifier first should minimise the window in which things
can go wrong, so that's about as much as we can reasonably do here. This
also revealed an additional race in assigning the global pointer too
late relative to the hotplug notifier, which gets fixed in the process.

Reported-by: Li, Meng <Meng.Li@windriver.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Robin Murphy 2019-04-16 16:24:24 +01:00 committed by Will Deacon
parent 3d659e7d65
commit 0d2e2a82d4
1 changed files with 12 additions and 9 deletions
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21
drivers/perf/arm-cci.c
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@ -1684,21 +1684,24 @@ static int cci_pmu_probe(struct platform_device *pdev)
raw_spin_lock_init(&cci_pmu->hw_events.pmu_lock);
mutex_init(&cci_pmu->reserve_mutex);
atomic_set(&cci_pmu->active_events, 0);
cci_pmu->cpu = get_cpu();
ret = cci_pmu_init(cci_pmu, pdev);
if (ret) {
put_cpu();
return ret;
}
cci_pmu->cpu = raw_smp_processor_id();
g_cci_pmu = cci_pmu;
cpuhp_setup_state_nocalls(CPUHP_AP_PERF_ARM_CCI_ONLINE,
"perf/arm/cci:online", NULL,
cci_pmu_offline_cpu);
put_cpu();
g_cci_pmu = cci_pmu;
ret = cci_pmu_init(cci_pmu, pdev);
if (ret)
goto error_pmu_init;
pr_info("ARM %s PMU driver probed", cci_pmu->model->name);
return 0;
error_pmu_init:
cpuhp_remove_state(CPUHP_AP_PERF_ARM_CCI_ONLINE);
g_cci_pmu = NULL;
return ret;
}
static int cci_pmu_remove(struct platform_device *pdev)