On 10/6/22 19:07, James Clark wrote:

On 29/09/2022 08:58, Anshuman Khandual wrote:

quoted

This adds arm pmu infrastrure to probe BRBE implementation's attributes via
driver exported callbacks later. The actual BRBE feature detection will be
added by the driver itself.

CPU specific BRBE entries, cycle count, format support gets detected during
PMU init. This information gets saved in per-cpu struct pmu_hw_events which
later helps in operating BRBE during a perf event context.

Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
 drivers/perf/arm_pmu_platform.c | 34 +++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/perf/arm_pmu_platform.c b/drivers/perf/arm_pmu_platform.c
index 933b96e243b8..acdc445081aa 100644
--- a/drivers/perf/arm_pmu_platform.c
+++ b/drivers/perf/arm_pmu_platform.c

@@ -172,6 +172,36 @@ static int armpmu_request_irqs(struct arm_pmu *armpmu)
 	return err;
 }
 
+static void arm_brbe_probe_cpu(void *info)
+{
+	struct pmu_hw_events *hw_events;
+	struct arm_pmu *armpmu = info;
+
+	/*
+	 * Return from here, if BRBE driver has not been
+	 * implemented for this PMU. This helps prevent
+	 * kernel crash later when brbe_probe() will be
+	 * called on the PMU.
+	 */
+	if (!armpmu->brbe_probe)
+		return;
+
+	hw_events = per_cpu_ptr(armpmu->hw_events, smp_processor_id());
+	armpmu->brbe_probe(hw_events);
+}
+
+static int armpmu_request_brbe(struct arm_pmu *armpmu)
+{
+	int cpu, err = 0;
+
+	for_each_cpu(cpu, &armpmu->supported_cpus) {
+		err = smp_call_function_single(cpu, arm_brbe_probe_cpu, armpmu, 1);

Hi Anshuman,

I have LOCKDEP on and the patchset applied to perf/core (82aad7ff7) on
git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git and I get
this:

   armv8-pmu pmu: hw perfevents: no interrupt-affinity property, guessing.
   brbe: implementation found on cpu 0

   =============================
   [ BUG: Invalid wait context ]
   6.0.0-rc7 #38 Not tainted
   -----------------------------
   kworker/u8:0/9 is trying to lock:
   ffff000800855898 (&port_lock_key){....}-{3:3}, at:
pl011_console_write+0x148/0x240
   other info that might help us debug this:
   context-{2:2}
   5 locks held by kworker/u8:0/9:
    #0: ffff00080032a138 ((wq_completion)eval_map_wq){+.+.}-{0:0}, at:
process_one_work+0x200/0x6b0
    #1: ffff80000807bde0
((work_completion)(&eval_map_work)){+.+.}-{0:0}, at:
process_one_work+0x200/0x6b0
    #2: ffff80000aa3db70 (trace_event_sem){+.+.}-{4:4}, at:
trace_event_eval_update+0x28/0x420
    #3: ffff80000a9afe58 (console_lock){+.+.}-{0:0}, at:
vprintk_emit+0x130/0x380
    #4: ffff80000a9aff78 (console_owner){-...}-{0:0}, at:
console_emit_next_record.constprop.0+0x128/0x338
   stack backtrace:
   CPU: 0 PID: 9 Comm: kworker/u8:0 Not tainted 6.0.0-rc7 #38
   Hardware name: Foundation-v8A (DT)
   Workqueue: eval_map_wq eval_map_work_func
   Call trace:
    dump_backtrace+0x114/0x120
    show_stack+0x20/0x58
    dump_stack_lvl+0x9c/0xd8
    dump_stack+0x18/0x34
    __lock_acquire+0x17cc/0x1920
    lock_acquire+0x138/0x3b8
    _raw_spin_lock+0x58/0x70
    pl011_console_write+0x148/0x240
    console_emit_next_record.constprop.0+0x194/0x338
    console_unlock+0x18c/0x208
    vprintk_emit+0x24c/0x380
    vprintk_default+0x40/0x50
    vprintk+0xd4/0xf0
    _printk+0x68/0x90
    arm64_pmu_brbe_probe+0x10c/0x128
    armv8pmu_brbe_probe+0x18/0x28
    arm_brbe_probe_cpu+0x44/0x58
    __flush_smp_call_function_queue+0x1d0/0x440
    generic_smp_call_function_single_interrupt+0x20/0x78
    ipi_handler+0x98/0x368
    handle_percpu_devid_irq+0xc0/0x3a8
    generic_handle_domain_irq+0x34/0x50
    gic_handle_irq+0x58/0x138
    call_on_irq_stack+0x2c/0x58
    do_interrupt_handler+0x88/0x90
    el1_interrupt+0x40/0x78
    el1h_64_irq_handler+0x18/0x28
    el1h_64_irq+0x64/0x68
    trace_event_eval_update+0x114/0x420
    eval_map_work_func+0x30/0x40
    process_one_work+0x298/0x6b0
    worker_thread+0x54/0x408
    kthread+0x118/0x128
    ret_from_fork+0x10/0x20
   brbe: implementation found on cpu 1
   brbe: implementation found on cpu 2
   brbe: implementation found on cpu 3

The LOCKDEP warnings are because of pr_warn/pr_info in arm64_pmu_brbe_probe()
which gets called from smp_call_function_single() context. I will drop these
prints, instead probably capture them in struct pmu_hw_events and display in
the caller itself.

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