Re: How is Code in do_sys_settimeofday() safe in case of SMP and Nest Kernel Path?

Dong Feng
2006-09-30T16:09:27Z

On Sat, 30 Sep 2006, Nick Piggin wrote
>
> You should write a patch and send it to Mister Morton.
>
> --
> SUSE Labs, Novell Inc.
> Send instant messages to your online friends http://au.messenger.yahoo.com
>
>

This is a patch for your review.

--- kernel/time.c.orig 2006-09-30 23:21:29.000000000 +0800
+++ kernel/time.c 2006-09-30 23:38:18.000000000 +0800
@@ -107,7 +107,16 @@ asmlinkage long sys_gettimeofday(struct
return -EFAULT;
}
if (unlikely(tz != NULL)) {
- if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
+ struct timezone ktz;
+ unsigned long seq;
+
+ do {
+ seq = read_seqbegin(&xtime_lock);
+ ktz.tz_minuteswest = sys_tz.tz_minuteswest;
+ ktz.tz_dsttime = sys_tz.tz_dsttime;
+ } while (unlikely(read_seqretry(&xtime_lock, seq)));
+
+ if (copy_to_user(tz, &ktz, sizeof(ktz)))
return -EFAULT;
}
return 0;
@@ -164,12 +173,16 @@ int do_sys_settimeofday(struct timespec

if (tz) {
/* SMP safe, global irq locking makes it work. */
- sys_tz = *tz;
- if (firsttime) {
- firsttime = 0;
- if (!tv)
- warp_clock();
+ write_seqlock_irq(&xtime_lock);
+ {
+ sys_tz = *tz;
+ if (firsttime) {
+ firsttime = 0;
+ if (!tv)
+ warp_clock();
+ }
}
+ write_sequnlock_irq(&xtime_lock);
}
if (tv)
{