linux-kernel - [PATCH] perf/x86/intel/cqm: Do not access cpu_data() from CPU_UP

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Date:	Thu,  6 Aug 2015 13:12:43 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...nel.org>, Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org,
	Matt Fleming <matt.fleming@...el.com>,
	Vikas Shivappa <vikas.shivappa@...el.com>,
	Kanaka Juvva <kanaka.d.juvva@...el.com>,
	<stable@...r.kernel.org>, Ashok Raj <ashok.raj@...el.com>
Subject: [PATCH] perf/x86/intel/cqm: Do not access cpu_data() from CPU_UP_PREPARE handler

From: Matt Fleming <matt.fleming@...el.com>

Tony reports that booting his 144-cpu machine with maxcpus=10 triggers
the following WARN_ON(),

[   21.045727] WARNING: CPU: 8 PID: 647 at arch/x86/kernel/cpu/perf_event_intel_cqm.c:1267 intel_cqm_cpu_prepare+0x75/0x90()
[   21.045744] CPU: 8 PID: 647 Comm: systemd-udevd Not tainted 4.2.0-rc4 #1
[   21.045745] Hardware name: Intel Corporation BRICKLAND/BRICKLAND, BIOS BRHSXSD1.86B.0066.R00.1506021730 06/02/2015
[   21.045747]  0000000000000000 0000000082771b09 ffff880856333ba8 ffffffff81669b67
[   21.045748]  0000000000000000 0000000000000000 ffff880856333be8 ffffffff8107b02a
[   21.045750]  ffff88085b789800 ffff88085f68a020 ffffffff819e2470 000000000000000a
[   21.045750] Call Trace:
[   21.045757]  [<ffffffff81669b67>] dump_stack+0x45/0x57
[   21.045759]  [<ffffffff8107b02a>] warn_slowpath_common+0x8a/0xc0
[   21.045761]  [<ffffffff8107b15a>] warn_slowpath_null+0x1a/0x20
[   21.045762]  [<ffffffff81036725>] intel_cqm_cpu_prepare+0x75/0x90
[   21.045764]  [<ffffffff81036872>] intel_cqm_cpu_notifier+0x42/0x160
[   21.045767]  [<ffffffff8109a33d>] notifier_call_chain+0x4d/0x80
[   21.045769]  [<ffffffff8109a44e>] __raw_notifier_call_chain+0xe/0x10
[   21.045770]  [<ffffffff8107b538>] _cpu_up+0xe8/0x190
[   21.045771]  [<ffffffff8107b65a>] cpu_up+0x7a/0xa0
[   21.045774]  [<ffffffff8165e920>] cpu_subsys_online+0x40/0x90
[   21.045777]  [<ffffffff81433b37>] device_online+0x67/0x90
[   21.045778]  [<ffffffff81433bea>] online_store+0x8a/0xa0
[   21.045782]  [<ffffffff81430e78>] dev_attr_store+0x18/0x30
[   21.045785]  [<ffffffff8126b6ba>] sysfs_kf_write+0x3a/0x50
[   21.045786]  [<ffffffff8126ad40>] kernfs_fop_write+0x120/0x170
[   21.045789]  [<ffffffff811f0b77>] __vfs_write+0x37/0x100
[   21.045791]  [<ffffffff811f38b8>] ? __sb_start_write+0x58/0x110
[   21.045795]  [<ffffffff81296d2d>] ? security_file_permission+0x3d/0xc0
[   21.045796]  [<ffffffff811f1279>] vfs_write+0xa9/0x190
[   21.045797]  [<ffffffff811f2075>] SyS_write+0x55/0xc0
[   21.045800]  [<ffffffff81067300>] ? do_page_fault+0x30/0x80
[   21.045804]  [<ffffffff816709ae>] entry_SYSCALL_64_fastpath+0x12/0x71
[   21.045805] ---[ end trace fe228b836d8af405 ]---

The root cause is that CPU_UP_PREPARE is completely the wrong notifier
action from which to access cpu_data() because smp_store_cpu_info()
won't have been executed by the target cpu at that point, which in turn
means that ->x86_cache_max_rmid and ->x86_cache_occ_scale haven't been
filled out.

Instead let's invoke our handler from CPU_STARTING and rename it
appropriately.

Reported-by: Tony Luck <tony.luck@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vikas Shivappa <vikas.shivappa@...el.com>
Cc: Kanaka Juvva <kanaka.d.juvva@...el.com>
Cc: <stable@...r.kernel.org>
Cc: Ashok Raj <ashok.raj@...el.com>
Signed-off-by: Matt Fleming <matt.fleming@...el.com>
---
 arch/x86/kernel/cpu/perf_event_intel_cqm.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
index 63eb68b73589..377e8f8ed391 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
@@ -1255,7 +1255,7 @@ static inline void cqm_pick_event_reader(int cpu)
 	cpumask_set_cpu(cpu, &cqm_cpumask);
 }
 
-static void intel_cqm_cpu_prepare(unsigned int cpu)
+static void intel_cqm_cpu_starting(unsigned int cpu)
 {
 	struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
@@ -1296,13 +1296,11 @@ static int intel_cqm_cpu_notifier(struct notifier_block *nb,
 	unsigned int cpu  = (unsigned long)hcpu;
 
 	switch (action & ~CPU_TASKS_FROZEN) {
-	case CPU_UP_PREPARE:
-		intel_cqm_cpu_prepare(cpu);
-		break;
 	case CPU_DOWN_PREPARE:
 		intel_cqm_cpu_exit(cpu);
 		break;
 	case CPU_STARTING:
+		intel_cqm_cpu_starting(cpu);
 		cqm_pick_event_reader(cpu);
 		break;
 	}
@@ -1373,7 +1371,7 @@ static int __init intel_cqm_init(void)
 		goto out;
 
 	for_each_online_cpu(i) {
-		intel_cqm_cpu_prepare(i);
+		intel_cqm_cpu_starting(i);
 		cqm_pick_event_reader(i);
 	}
 
-- 
2.1.0

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