linux-kernel - [PATCH v2] clocksource/arm_arch

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Message-Id: <1543877121-4098-1-git-send-email-cai@gmx.us>
Date:   Mon,  3 Dec 2018 17:45:21 -0500
From:   Qian Cai <cai@....us>
To:     mark.rutland@....com, marc.zyngier@....com
Cc:     daniel.lezcano@...aro.org, tglx@...utronix.de,
        peterz@...radead.org, mingo@...nel.org, longman@...hat.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Qian Cai <cai@....us>
Subject: [PATCH v2] clocksource/arm_arch_timer: fix a lockdep warning

Booting this Huawei TaiShan 2280 arm64 server generated this lockdep
warning.

[    0.000000]  lockdep_assert_cpus_held+0x50/0x60
[    0.000000]  static_key_enable_cpuslocked+0x30/0xe8
[    0.000000]  arch_timer_check_ool_workaround+0x128/0x2d0
[    0.000000]  arch_timer_acpi_init+0x274/0x6ac
[    0.000000]  acpi_table_parse+0x1ac/0x218
[    0.000000]  __acpi_probe_device_table+0x164/0x1ec
[    0.000000]  timer_probe+0x1bc/0x254
[    0.000000]  time_init+0x44/0x98
[    0.000000]  start_kernel+0x4ec/0x7d4

This is due to the commit cb538267ea1e ("jump_label/lockdep: Assert we hold
the hotplug lock for _cpuslocked() operations").

Since it is applying a global workaround to all CPUs here, it did not hold
any CPU locks in this path.

arch_timer_acpi_init
  arch_timer_check_ool_workaround(ate_match_acpi_oem_info, table)
    arch_timer_enable_workaround(wa, local = false)
      for_each_possible_cpu()
	per_cpu()

When hot-add a CPU, it will go with a slightly different route.

arch_timer_starting_cpu
  __arch_timer_setup
    arch_timer_check_ool_workaround(ate_match_local_cap_id, NULL)
      arch_timer_enable_workaround(wa, local = true)
        __this_cpu_write()

Hence, deal with them differently.

Fixes: 450f9689f294 (clocksource/arm_arch_timer: Use
	static_branch_enable_cpuslocked())
Signed-off-by: Qian Cai <cai@....us>
---

Changes since v1:
* Fixed the root cause instead of a workaround.

 drivers/clocksource/arm_arch_timer.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 9a7d4dc00b6e..81dca7d31d13 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -492,18 +492,21 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa
 
 	if (local) {
 		__this_cpu_write(timer_unstable_counter_workaround, wa);
+
+		/*
+		 * Use the locked version, as we're called from the CPU
+		 * hotplug framework. Otherwise, we end-up in
+		 * deadlock-land.
+		 */
+		static_branch_enable_cpuslocked(&arch_timer_read_ool_enabled);
 	} else {
 		for_each_possible_cpu(i)
 			per_cpu(timer_unstable_counter_workaround, i) = wa;
+		/* A global workaround is not on the CPU hotplug path. */
+		static_branch_enable(&arch_timer_read_ool_enabled);
 	}
 
 	/*
-	 * Use the locked version, as we're called from the CPU
-	 * hotplug framework. Otherwise, we end-up in deadlock-land.
-	 */
-	static_branch_enable_cpuslocked(&arch_timer_read_ool_enabled);
-
-	/*
 	 * Don't use the vdso fastpath if errata require using the
 	 * out-of-line counter accessor. We may change our mind pretty
 	 * late in the game (with a per-CPU erratum, for example), so
-- 
1.8.3.1