time: create __getnstimeofday for WARNless calls

The pstore RAM backend can get called during resume, and must be defensive
against a suspended time source. Expose getnstimeofday logic that returns
an error instead of a WARN. This can be detected and the timestamp can
be zeroed out.

Reported-by: Doug Anderson <dianders@chromium.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 1a4f6da..dacfe78 100644 (file)
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -168,12 +168,16 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
 static size_t ramoops_write_kmsg_hdr(struct persistent_ram_zone *prz)
 {
        char *hdr;
-       struct timeval timestamp;
+       struct timespec timestamp;
        size_t len;
 
-       do_gettimeofday(&timestamp);
+       /* Report zeroed timestamp if called before timekeeping has resumed. */
+       if (__getnstimeofday(&timestamp)) {
+               timestamp.tv_sec = 0;
+               timestamp.tv_nsec = 0;
+       }
        hdr = kasprintf(GFP_ATOMIC, RAMOOPS_KERNMSG_HDR "%lu.%lu\n",
-               (long)timestamp.tv_sec, (long)timestamp.tv_usec);
+               (long)timestamp.tv_sec, (long)(timestamp.tv_nsec / 1000));
        WARN_ON_ONCE(!hdr);
        len = hdr ? strlen(hdr) : 0;
        persistent_ram_write(prz, hdr, len);

diff --git a/include/linux/time.h b/include/linux/time.h
index 4d358e9..0015aea 100644 (file)
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -158,6 +158,7 @@ extern int do_setitimer(int which, struct itimerval *value,
                        struct itimerval *ovalue);
 extern unsigned int alarm_setitimer(unsigned int seconds);
 extern int do_getitimer(int which, struct itimerval *value);
+extern int __getnstimeofday(struct timespec *tv);
 extern void getnstimeofday(struct timespec *tv);
 extern void getrawmonotonic(struct timespec *ts);
 extern void getnstime_raw_and_real(struct timespec *ts_raw,

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4c7de02..dfc7f87 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -214,19 +214,18 @@ static void timekeeping_forward_now(struct timekeeper *tk)
 }
 
 /**
- * getnstimeofday - Returns the time of day in a timespec
+ * __getnstimeofday - Returns the time of day in a timespec.
  * @ts:                pointer to the timespec to be set
  *
- * Returns the time of day in a timespec.
+ * Updates the time of day in the timespec.
+ * Returns 0 on success, or -ve when suspended (timespec will be undefined).
  */
-void getnstimeofday(struct timespec *ts)
+int __getnstimeofday(struct timespec *ts)
 {
        struct timekeeper *tk = &timekeeper;
        unsigned long seq;
        s64 nsecs = 0;
 
-       WARN_ON(timekeeping_suspended);
-
        do {
                seq = read_seqbegin(&tk->lock);
 
@@ -237,6 +236,26 @@ void getnstimeofday(struct timespec *ts)
 
        ts->tv_nsec = 0;
        timespec_add_ns(ts, nsecs);
+
+       /*
+        * Do not bail out early, in case there were callers still using
+        * the value, even in the face of the WARN_ON.
+        */
+       if (unlikely(timekeeping_suspended))
+               return -EAGAIN;
+       return 0;
+}
+EXPORT_SYMBOL(__getnstimeofday);
+
+/**
+ * getnstimeofday - Returns the time of day in a timespec.
+ * @ts:                pointer to the timespec to be set
+ *
+ * Returns the time of day in a timespec (WARN if suspended).
+ */
+void getnstimeofday(struct timespec *ts)
+{
+       WARN_ON(__getnstimeofday(ts));
 }
 EXPORT_SYMBOL(getnstimeofday);