On Mon, May 05, 2014 at 03:45:28PM +0000, Bryan Evenson wrote:
> I did get strace loaded on my system and I used that to get a better
> understanding of where the error occurs. I modified my test script as
> follows:
> ----------
> #!/bin/sh
> i=0
> while [ 1 ]; do
> strace -f -o /home/root/hwclock_output_"$$_$i".txt /sbin/hwclock -w -u
> : $((i++))
> sleep 1;
> done
> ----------
>
> Again, on my system I was able to get an instance of hwclock to enter an
> uninterruptable sleep and hang within seconds when I ran two instances of the
> test script. By checking the PID of the hung process and the PIDs in the
> output files, I found the strace of the hung process, which is shown below.
>
<snip>
> 1808 ioctl(3, RTC_SET_TIME, {tm_sec=7, tm_min=5, tm_hour=14, tm_mday=5,
> tm_mon=4, tm_year=114, ...}
> ----------
>
> And here is the output from the hwclock instance that occurred from the other
> test script just before this one:
>
> ----------
<snip>
> 1799 ioctl(3, RTC_SET_TIME, {tm_sec=7, tm_min=5, tm_hour=14, tm_mday=5,
> tm_mon=4, tm_year=114, ...}) = 0
> 1799 exit_group(0) = ?
> 1799 +++ exited with 0 +++
> ----------
>
> So on my system, hwclock is hanging on the ioctl to set the time.
> Both the instance that set the time and the one that could not set
> the time are trying to set the RTC to the same time. So I'm assuming
> from this output that there is something going wrong with the ioctl on
> my RTC driver when two separate processes attempt to set the time at
> the same time. If I'm interpreting this correctly, I need to track
> down what the RTC driver is doing wrong with the RTC_SET_TIME ioctl.
>
Well, having two processes trying to set time is rather nonsensical.
I suppose that the _right_ thing for the kernel to do would be have one
block until the other finished, but...it makes sense to lock the fd.
So does the patch I'm attaching work for you?
HTH,
Isaac Dunham
diff --git a/util-linux/hwclock.c b/util-linux/hwclock.c
index 3f53155..8fed1ca 100644
--- a/util-linux/hwclock.c
+++ b/util-linux/hwclock.c
@@ -10,6 +10,7 @@
#include "libbb.h"
/* After libbb.h, since it needs sys/types.h on some systems */
#include <sys/utsname.h>
+#include <sys/file.h>
#include "rtc_.h"
/* diff code is disabled: it's not sys/hw clock diff, it's some useless
@@ -227,7 +228,10 @@ static void from_sys_clock(const char **pp_rtcname, int
utc)
#endif
tm_time.tm_isdst = 0;
+ if (flock(rtc, LOCK_EX))
+ bb_perror_msg_and_die("rtc open");
xioctl(rtc, RTC_SET_TIME, &tm_time);
+ flock(rtc, LOCK_UN);
if (ENABLE_FEATURE_CLEAN_UP)
close(rtc);
_______________________________________________
busybox mailing list
[email protected]
http://lists.busybox.net/mailman/listinfo/busybox
