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Subject[PATCH] intel_pstate: fix race condition in intel_pstate_init()
There is a race condition in the intel pstate driver initialization:
the cpufreq_register_driver() function creates a timer that makes use of the
energy_divisor variable (intel_pstate_timer_func), the problem is that energy_divisor is initialized
*after* the call to cpufreq_register_driver().

This patch fixes the bug by initializing energy_divisor before the
call to cpufreq_register_driver().


[ 2.351047] Intel pstate controlling: cpu 2
[ 2.355271] divide error: 0000 [#1] SMP
[ 2.359222] Modules linked in:
[ 2.362291] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.14.0-rc1-linux-mainline+ #7
[ 2.369933] Hardware name: wortmann To be filled by O.E.M./P8B-M Series, BIOS 6103 12/06/2012
[ 2.378441] task: ffff880223948000 ti: ffff880223944000 task.ti: ffff880223944000
[ 2.385912] RIP: 0010:[<ffffffff81548b07>] [<ffffffff81548b07>] intel_pstate_timer_func+0x2b7/0x430
[ 2.395060] RSP: 0000:ffff880226e03d58 EFLAGS: 00010246
[ 2.400363] RAX: 0000000006130063 RBX: ffff88022191b800 RCX: 0000000000000199
[ 2.407486] RDX: 0000000000000000 RSI: 0000000000002000 RDI: 0000000000000199
[ 2.414608] RBP: ffff880226e03dd8 R08: ffff88022191b850 R09: ffff880223948cc8
[ 2.421731] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002
[ 2.428854] R13: 0000000006130063 R14: 0000003b3a91a54e R15: ffff880226e03da4
[ 2.435984] FS: 0000000000000000(0000) GS:ffff880226e00000(0000) knlGS:0000000000000000
[ 2.444060] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2.449794] CR2: ffff88022ffff000 CR3: 0000000001a0e000 CR4: 00000000000407f0
[ 2.456917] Stack:
[ 2.458927] ffff880226e03dd8 0000000000000246 0000000000000000 ffffffff8108a0c0
[ 2.466380] 0000000000000000 ffffffff82dc18d0 ffff880226e03d98 0000000000000246
[ 2.473832] 0000000026e03da8 0000000026e03e08 0000000000000038 ffff88022191b848
[ 2.481281] Call Trace:
[ 2.483725] <IRQ>
[ 2.485651] [<ffffffff8108a0c0>] ? cascade+0xb0/0xb0
[ 2.490912] [<ffffffff81548850>] ? intel_pstate_platform_pwr_mgmt_exists+0x1e0/0x1e0
[ 2.498736] [<ffffffff8108a158>] call_timer_fn+0x98/0x260
[ 2.504218] [<ffffffff8108a0c0>] ? cascade+0xb0/0xb0
[ 2.509263] [<ffffffff816de600>] ? _raw_spin_unlock_irq+0x30/0x50
[ 2.515439] [<ffffffff8108bc78>] run_timer_softirq+0x298/0x310
[ 2.521351] [<ffffffff81100eef>] ? rcu_irq_exit+0x8f/0xe0
[ 2.526833] [<ffffffff816debf3>] ? retint_restore_args+0x13/0x13
[ 2.532919] [<ffffffff81548850>] ? intel_pstate_platform_pwr_mgmt_exists+0x1e0/0x1e0
[ 2.540741] [<ffffffff81082584>] __do_softirq+0x144/0x4f0
[ 2.546217] [<ffffffff81082ebd>] irq_exit+0x14d/0x180
[ 2.551346] [<ffffffff816eb2da>] smp_apic_timer_interrupt+0x4a/0x60
[ 2.557688] [<ffffffff816e9bf2>] apic_timer_interrupt+0x72/0x80
[ 2.563685] <EOI>
[ 2.565608] [<ffffffff810e2ff0>] ? mark_held_locks+0x90/0x150
[ 2.571639] [<ffffffff810f5070>] ? vprintk_emit+0x1c0/0x610
[ 2.577299] [<ffffffff816de660>] ? _raw_spin_unlock_irqrestore+0x40/0x80
[ 2.584083] [<ffffffff816d74ea>] printk+0x77/0x79
[ 2.588873] [<ffffffff815479bc>] ? core_get_turbo_pstate+0x3c/0x60
[ 2.595139] [<ffffffff815481a5>] intel_pstate_init_cpu+0x395/0x3a0
[ 2.601404] [<ffffffff815481cb>] intel_pstate_cpu_init+0x1b/0x100
[ 2.607580] [<ffffffff81543933>] __cpufreq_add_dev+0x213/0x780
[ 2.613491] [<ffffffff816cd6fe>] ? klist_next+0x8e/0x120
[ 2.618887] [<ffffffff81543eb0>] cpufreq_add_dev+0x10/0x20
[ 2.624451] [<ffffffff8145d921>] subsys_interface_register+0xb1/0xe0
[ 2.630880] [<ffffffff810e345d>] ? trace_hardirqs_on+0xd/0x10
[ 2.636711] [<ffffffff81541a1e>] cpufreq_register_driver+0xfe/0x2a0
[ 2.643055] [<ffffffff81ddd383>] intel_pstate_init+0x14a/0x310
[ 2.648972] [<ffffffff816d9cbe>] ? mutex_unlock+0xe/0x10
[ 2.654361] [<ffffffff81ddd239>] ? intel_pstate_setup+0x2e/0x2e
[ 2.660357] [<ffffffff810020da>] do_one_initcall+0xda/0x180
[ 2.666008] [<ffffffff81d8ed9b>] ? kernel_init_freeable+0x31a/0x31a
[ 2.672357] [<ffffffff81d8ea5e>] do_basic_setup+0x9d/0xc0
[ 2.677833] [<ffffffff81d8ed9b>] ? kernel_init_freeable+0x31a/0x31a
[ 2.684176] [<ffffffff81d8ed18>] kernel_init_freeable+0x297/0x31a
[ 2.690345] [<ffffffff816cddce>] ? kernel_init+0xe/0xf0
[ 2.695648] [<ffffffff810e3385>] ? trace_hardirqs_on_caller+0x105/0x1d0
[ 2.702339] [<ffffffff816cddc0>] ? rest_init+0x170/0x170
[ 2.707734] [<ffffffff816cddce>] kernel_init+0xe/0xf0
[ 2.712866] [<ffffffff816e8e3c>] ret_from_fork+0x7c/0xb0
[ 2.718262] [<ffffffff816cddc0>] ? rest_init+0x170/0x170
[ 2.723651] Code: c8 00 00 00 48 89 df 01 d6 e8 b6 f1 ff ff eb 0e 0f 1f 40 00 29 d6 48 89 df e8 a6 f1 ff ff 4b 8d 04 a4 31 d2 4c 8d 04 c3 4c 89 e8 <48> f7 35 fa 8d 9b 01 45 8b b8 40 01 00 00 41 89 c1 49 8b 80 28
[ 2.743596] RIP [<ffffffff81548b07>] intel_pstate_timer_func+0x2b7/0x430
[ 2.750390] RSP <ffff880226e03d58>
[ 2.751934] tsc: Refined TSC clocksource calibration: 3092.975 MHz
[ 2.760048] divide error: 0000 [#2] [ 2.760064] ---[ end trace b87c91b37801378a ]---
[ 2.761931] Kernel panic - not syncing: Fatal exception in interrupt

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
---
drivers/cpufreq/intel_pstate.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 79606f4..bc04e73 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -956,13 +956,13 @@ static int __init intel_pstate_init(void)
if (!all_cpu_data)
return -ENOMEM;

+ rdmsrl(MSR_RAPL_POWER_UNIT, units);
+ energy_divisor = 1 << ((units >> 8) & 0x1f); /* bits{12:8} */
+
rc = cpufreq_register_driver(&intel_pstate_driver);
if (rc)
goto out;

- rdmsrl(MSR_RAPL_POWER_UNIT, units);
- energy_divisor = 1 << ((units >> 8) & 0x1f); /* bits{12:8} */
-
intel_pstate_debug_expose_params();
intel_pstate_sysfs_expose_params();

--
Maurizio Lombardi

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