linux-kernel - [PATCH 9/10] work_on_cpu: use on drivers/firmware/dcdbas.c

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Date:	Thu, 05 Mar 2009 17:27:23 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	linux-kernel@...r.kernel.org
Cc:	Douglas_Warzecha@...l.com
Subject: [PATCH 9/10] work_on_cpu: use on drivers/firmware/dcdbas.c


Impact: don't play with current's cpumask

It's generally a very bad idea to mug some process's cpumask: it could
legitimately and reasonably be changed by root, which could break us
(if done before our code) or them (if we restore the wrong value).

So we use work_on_cpu instead of cpumask games.

Note one subtle change.  If we can't get to CPU 0 for some reason, the
return will be -EINVAL not -EBUSY.  We could fix this in the
caller?  ie:

	return work_on_cpu(0, generate_smi, smi_cmd) == 0 ? 0 : -EBUSY;

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Cc: Matthew Garrett <mjg59@...f.ucam.org>
Cc: Matt Domsch <Matt_Domsch@...l.com>
Cc: Douglas_Warzecha@...l.com
---
 drivers/firmware/dcdbas.c |   46 +++++++++++++++++++---------------------------
 1 file changed, 19 insertions(+), 27 deletions(-)

diff --git a/drivers/firmware/dcdbas.c b/drivers/firmware/dcdbas.c
--- a/drivers/firmware/dcdbas.c
+++ b/drivers/firmware/dcdbas.c
@@ -237,31 +237,9 @@ static ssize_t host_control_on_shutdown_
 	return count;
 }
 
-/**
- * dcdbas_smi_request: generate SMI request
- *
- * Called with smi_data_lock.
- */
-int dcdbas_smi_request(struct smi_cmd *smi_cmd)
+static long generate_smi(void *_smi_cmd)
 {
-	cpumask_t old_mask;
-	int ret = 0;
-
-	if (smi_cmd->magic != SMI_CMD_MAGIC) {
-		dev_info(&dcdbas_pdev->dev, "%s: invalid magic value\n",
-			 __func__);
-		return -EBADR;
-	}
-
-	/* SMI requires CPU 0 */
-	old_mask = current->cpus_allowed;
-	set_cpus_allowed_ptr(current, &cpumask_of_cpu(0));
-	if (smp_processor_id() != 0) {
-		dev_dbg(&dcdbas_pdev->dev, "%s: failed to get CPU 0\n",
-			__func__);
-		ret = -EBUSY;
-		goto out;
-	}
+	struct smi_cmd *smi_cmd = _smi_cmd;
 
 	/* generate SMI */
 	asm volatile (
@@ -273,10 +251,24 @@ int dcdbas_smi_request(struct smi_cmd *s
 		  "c" (smi_cmd->ecx)
 		: "memory"
 	);
+	return 0;
+}
 
-out:
-	set_cpus_allowed_ptr(current, &old_mask);
-	return ret;
+/**
+ * dcdbas_smi_request: generate SMI request
+ *
+ * Called with smi_data_lock.
+ */
+int dcdbas_smi_request(struct smi_cmd *smi_cmd)
+{
+	if (smi_cmd->magic != SMI_CMD_MAGIC) {
+		dev_info(&dcdbas_pdev->dev, "%s: invalid magic value\n",
+			 __func__);
+		return -EBADR;
+	}
+
+	/* SMI requires CPU 0 */
+	return work_on_cpu(0, generate_smi, smi_cmd);
 }
 
 /**

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