s390/stp: add locking to sysfs functions

BugLink: https://bugs.launchpad.net/bugs/1904450
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: William Breathitt Gray <william.gray@canonical.com>

diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index 8ea9db599d38d3ccfe49fcabd149c145d5282436..11c32b228f518bc7ee6ea7a146fe70e2f075f3ec 100644 (file)
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -354,8 +354,9 @@ 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
@@ -592,6 +593,22 @@ 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;
@@ -613,8 +630,7 @@ 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;
                        }
@@ -659,7 +675,7 @@ 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;
 
@@ -696,10 +712,14 @@ static ssize_t stp_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(ctn_id, 0400, stp_ctn_id_show, NULL);
@@ -708,9 +728,13 @@ static ssize_t stp_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(ctn_type, 0400, stp_ctn_type_show, NULL);
@@ -719,9 +743,13 @@ static ssize_t stp_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(dst_offset, 0400, stp_dst_offset_show, NULL);
@@ -730,9 +758,13 @@ static ssize_t stp_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(leap_seconds, 0400, stp_leap_seconds_show, NULL);
@@ -741,9 +773,13 @@ static ssize_t stp_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(stratum, 0400, stp_stratum_show, NULL);
@@ -752,9 +788,13 @@ static ssize_t stp_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(time_offset, 0400, stp_time_offset_show, NULL);
@@ -763,9 +803,13 @@ static ssize_t stp_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(time_zone_offset, 0400,
@@ -775,9 +819,13 @@ static ssize_t stp_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(timing_mode, 0400, stp_timing_mode_show, NULL);
@@ -786,9 +834,13 @@ static ssize_t stp_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(timing_state, 0400, stp_timing_state_show, NULL);