[PATCH 4.14 091/125] s390/stp: add locking to sysfs functions

Greg Kroah-Hartman
2020-11-03T21:12:16Z

From: Sven Schnelle <svens@linux.ibm.com>

commit b3bd02495cb339124f13135d51940cf48d83e5cb upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/kernel/time.c | 118 ++++++++++++++++++++++++++++++++++--------------
1 file changed, 85 insertions(+), 33 deletions(-)

--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -347,8 +347,9 @@ static DEFINE_PER_CPU(atomic_t, clock_sy
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
@@ -585,6 +586,22 @@ 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;
@@ -606,8 +623,7 @@ 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;
}
@@ -652,7 +668,7 @@ static void stp_work_fn(struct work_stru
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;

@@ -689,10 +705,14 @@ static ssize_t stp_ctn_id_show(struct de
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(ctn_id, 0400, stp_ctn_id_show, NULL);
@@ -701,9 +721,13 @@ static ssize_t stp_ctn_type_show(struct
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(ctn_type, 0400, stp_ctn_type_show, NULL);
@@ -712,9 +736,13 @@ static ssize_t stp_dst_offset_show(struc
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(dst_offset, 0400, stp_dst_offset_show, NULL);
@@ -723,9 +751,13 @@ static ssize_t stp_leap_seconds_show(str
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(leap_seconds, 0400, stp_leap_seconds_show, NULL);
@@ -734,9 +766,13 @@ static ssize_t stp_stratum_show(struct d
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(stratum, 0400, stp_stratum_show, NULL);
@@ -745,9 +781,13 @@ static ssize_t stp_time_offset_show(stru
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(time_offset, 0400, stp_time_offset_show, NULL);
@@ -756,9 +796,13 @@ static ssize_t stp_time_zone_offset_show
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(time_zone_offset, 0400,
@@ -768,9 +812,13 @@ static ssize_t stp_timing_mode_show(stru
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(timing_mode, 0400, stp_timing_mode_show, NULL);
@@ -779,9 +827,13 @@ static ssize_t stp_timing_state_show(str
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(timing_state, 0400, stp_timing_state_show, NULL);