linux-kernel - Re: [PATCH] hwmon: (fam15h_power) Disable preemption when reading registers

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Date:	Thu, 2 Jun 2016 09:26:19 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-hwmon@...r.kernel.org,
	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Rui Huang <ray.huang@....com>,
	Sherry Hurwitz <sherry.hurwitz@....com>
Subject: Re: [PATCH] hwmon: (fam15h_power) Disable preemption when reading
 registers

On Wed, Jun 01, 2016 at 11:15:09AM -0700, Guenter Roeck wrote:
> It would be great if you can add at least part of the BUG message as well
> as a Fixes: tag into the patch description.

How's that:

---
From: Borislav Petkov <bp@...e.de>
Date: Wed, 1 Jun 2016 11:36:13 +0200
Subject: [PATCH] hwmon: (fam15h_power) Disable preemption when reading registers

We need to read a bunch of registers on each compute unit and possibly
on the current CPU too. Disable preemption around it. Otherwise, you
get:

  BUG: using smp_processor_id() in preemptible [00000000] code: systemd-udevd/327
  caller is read_registers+0x6a/0x110 [fam15h_power]
  CPU: 3 PID: 327 Comm: systemd-udevd Not tainted 4.7.0-rc1+ #4
  Hardware name: HP HP EliteBook 745 G3/807E, BIOS N73 Ver. 01.08 01/28/2016
  ...

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Rui Huang <ray.huang@....com>
Cc: Sherry Hurwitz <sherry.hurwitz@....com>
Cc: Guenter Roeck <linux@...ck-us.net>
Fixes: fa7943449943 ("hwmon: (fam15h_power) Add compute unit accumulated power")
---
 drivers/hwmon/fam15h_power.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/fam15h_power.c b/drivers/hwmon/fam15h_power.c
index eb97a9241d17..69bb810f528b 100644
--- a/drivers/hwmon/fam15h_power.c
+++ b/drivers/hwmon/fam15h_power.c
@@ -172,9 +172,9 @@ static void do_read_registers_on_cu(void *_data)
  */
 static int read_registers(struct fam15h_power_data *data)
 {
-	int this_cpu, ret, cpu;
 	int core, this_core;
 	cpumask_var_t mask;
+	int ret, cpu;
 
 	ret = zalloc_cpumask_var(&mask, GFP_KERNEL);
 	if (!ret)
@@ -183,7 +183,6 @@ static int read_registers(struct fam15h_power_data *data)
 	memset(data->cu_on, 0, sizeof(int) * MAX_CUS);
 
 	get_online_cpus();
-	this_cpu = smp_processor_id();
 
 	/*
 	 * Choose the first online core of each compute unit, and then
@@ -205,10 +204,13 @@ static int read_registers(struct fam15h_power_data *data)
 		cpumask_set_cpu(cpumask_any(topology_sibling_cpumask(cpu)), mask);
 	}
 
-	if (cpumask_test_cpu(this_cpu, mask))
+	preempt_disable();
+	smp_call_function_many(mask, do_read_registers_on_cu, data, true);
+
+	if (cpumask_test_cpu(smp_processor_id(), mask))
 		do_read_registers_on_cu(data);
 
-	smp_call_function_many(mask, do_read_registers_on_cu, data, true);
+	preempt_enable();
 	put_online_cpus();
 
 	free_cpumask_var(mask);
-- 
2.7.3

-- 
Regards/Gruss,
    Boris.

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