s390/stp: add locking to sysfs functions

The sysfs function might race with stp_work_fn. To prevent that,
add the required locking. Another issue is that the sysfs functions
are checking the stp_online flag, but this flag just holds the user
setting whether STP is enabled. Add a flag to clock_sync_flag whether
stp_info holds valid data and use that instead.

Cc: stable@vger.kernel.org
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/time.c

@@ -299,8 +299,9 @@ static DEFINE_PER_CPU(atomic_t, clock_sync_word);
 static DEFINE_MUTEX(clock_sync_mutex);
 static unsigned long clock_sync_flags;
 
-#define CLOCK_SYNC_HAS_STP	0
-#define CLOCK_SYNC_STP		1
+#define CLOCK_SYNC_HAS_STP		0
+#define CLOCK_SYNC_STP			1
+#define CLOCK_SYNC_STPINFO_VALID	2
 
 /*
  * The get_clock function for the physical clock. It will get the current
@@ -535,6 +536,22 @@ void stp_queue_work(void)
 	queue_work(time_sync_wq, &stp_work);
 }
 
+static int __store_stpinfo(void)
+{
+	int rc = chsc_sstpi(stp_page, &stp_info, sizeof(struct stp_sstpi));
+
+	if (rc)
+		clear_bit(CLOCK_SYNC_STPINFO_VALID, &clock_sync_flags);
+	else
+		set_bit(CLOCK_SYNC_STPINFO_VALID, &clock_sync_flags);
+	return rc;
+}
+
+static int stpinfo_valid(void)
+{
+	return stp_online && test_bit(CLOCK_SYNC_STPINFO_VALID, &clock_sync_flags);
+}
+
 static int stp_sync_clock(void *data)
 {
 	struct clock_sync_data *sync = data;
@@ -557,8 +574,7 @@ static int stp_sync_clock(void *data)
 			if (rc == 0) {
 				sync->clock_delta = clock_delta;
 				clock_sync_global(clock_delta);
-				rc = chsc_sstpi(stp_page, &stp_info,
-						sizeof(struct stp_sstpi));
+				rc = __store_stpinfo();
 				if (rc == 0 && stp_info.tmd != 2)
 					rc = -EAGAIN;
 			}
@@ -604,7 +620,7 @@ static void stp_work_fn(struct work_struct *work)
 	if (rc)
 		goto out_unlock;
 
-	rc = chsc_sstpi(stp_page, &stp_info, sizeof(struct stp_sstpi));
+	rc = __store_stpinfo();
 	if (rc || stp_info.c == 0)
 		goto out_unlock;
 
@@ -641,10 +657,14 @@ static ssize_t ctn_id_show(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	if (!stp_online)
-		return -ENODATA;
-	return sprintf(buf, "%016llx\n",
-		       *(unsigned long long *) stp_info.ctnid);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid())
+		ret = sprintf(buf, "%016llx\n",
+			      *(unsigned long long *) stp_info.ctnid);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(ctn_id);
@@ -653,9 +673,13 @@ static ssize_t ctn_type_show(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	if (!stp_online)
-		return -ENODATA;
-	return sprintf(buf, "%i\n", stp_info.ctn);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid())
+		ret = sprintf(buf, "%i\n", stp_info.ctn);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(ctn_type);
@@ -664,9 +688,13 @@ static ssize_t dst_offset_show(struct device *dev,
 				   struct device_attribute *attr,
 				   char *buf)
 {
-	if (!stp_online || !(stp_info.vbits & 0x2000))
-		return -ENODATA;
-	return sprintf(buf, "%i\n", (int)(s16) stp_info.dsto);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid() && (stp_info.vbits & 0x2000))
+		ret = sprintf(buf, "%i\n", (int)(s16) stp_info.dsto);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(dst_offset);
@@ -675,9 +703,13 @@ static ssize_t leap_seconds_show(struct device *dev,
 					struct device_attribute *attr,
 					char *buf)
 {
-	if (!stp_online || !(stp_info.vbits & 0x8000))
-		return -ENODATA;
-	return sprintf(buf, "%i\n", (int)(s16) stp_info.leaps);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid() && (stp_info.vbits & 0x8000))
+		ret = sprintf(buf, "%i\n", (int)(s16) stp_info.leaps);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(leap_seconds);
@@ -686,9 +718,13 @@ static ssize_t stratum_show(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	if (!stp_online)
-		return -ENODATA;
-	return sprintf(buf, "%i\n", (int)(s16) stp_info.stratum);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid())
+		ret = sprintf(buf, "%i\n", (int)(s16) stp_info.stratum);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(stratum);
@@ -697,9 +733,13 @@ static ssize_t time_offset_show(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	if (!stp_online || !(stp_info.vbits & 0x0800))
-		return -ENODATA;
-	return sprintf(buf, "%i\n", (int) stp_info.tto);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid() && (stp_info.vbits & 0x0800))
+		ret = sprintf(buf, "%i\n", (int) stp_info.tto);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(time_offset);
@@ -708,9 +748,13 @@ static ssize_t time_zone_offset_show(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	if (!stp_online || !(stp_info.vbits & 0x4000))
-		return -ENODATA;
-	return sprintf(buf, "%i\n", (int)(s16) stp_info.tzo);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid() && (stp_info.vbits & 0x4000))
+		ret = sprintf(buf, "%i\n", (int)(s16) stp_info.tzo);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(time_zone_offset);
@@ -719,9 +763,13 @@ static ssize_t timing_mode_show(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	if (!stp_online)
-		return -ENODATA;
-	return sprintf(buf, "%i\n", stp_info.tmd);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid())
+		ret = sprintf(buf, "%i\n", stp_info.tmd);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(timing_mode);
@@ -730,9 +778,13 @@ static ssize_t timing_state_show(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	if (!stp_online)
-		return -ENODATA;
-	return sprintf(buf, "%i\n", stp_info.tst);
+	ssize_t ret = -ENODATA;
+
+	mutex_lock(&stp_work_mutex);
+	if (stpinfo_valid())
+		ret = sprintf(buf, "%i\n", stp_info.tst);
+	mutex_unlock(&stp_work_mutex);
+	return ret;
 }
 
 static DEVICE_ATTR_RO(timing_state);