Re: [PATCH] fix gettimeofday vs. update_gtod race
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: 2006-08-16 23:49:04
On Fri, 2006-08-11 at 15:41 -0500, Nathan Lynch wrote:
+ /* Sampling the time base must be done after loading + * do_gtod.varp in order to avoid racing with update_gtod. + */ + rmb(); + tb_ticks = get_tb() - temp_varp->tb_orig_stamp;
The barrier isn't necessary and the race not completely closed imho... I need to think about it a bit more closely but what about instead just check if tb_ticks goes negative, and if yes, just do get_tb() again ? That might be faster than having a sync in there and should still be correct.
quoted hunk ↗ jump to hunk
temp_tb_to_xs = temp_varp->tb_to_xs; temp_stamp_xsec = temp_varp->stamp_xsec; xsec = temp_stamp_xsec + mulhdu(tb_ticks, temp_tb_to_xs);@@ -464,7 +469,7 @@ void do_gettimeofday(struct timeval *tv) tv->tv_usec = usec; return; } - __do_gettimeofday(tv, get_tb()); + __do_gettimeofday(tv); } EXPORT_SYMBOL(do_gettimeofday);_______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev