[ Upstream commit 0d2e2a82d4de298d006bf8eddc86829e3c7da820 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/perf/arm-cci.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/drivers/perf/arm-cci.c b/drivers/perf/arm-cci.c index bfd03e0233084..8f8606b9bc9ee 100644 --- a/drivers/perf/arm-cci.c +++ b/drivers/perf/arm-cci.c @@ -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)