linux-kernel - Re: Possible clocksource wrapping issues w/ new vdso clock

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Date:	Mon, 23 Jul 2007 11:04:55 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Andi Kleen <ak@...e.de>
Cc:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: Possible clocksource wrapping issues w/ new vdso
	clock_gettime() code?

On Mon, 2007-07-23 at 10:59 -0700, john stultz wrote:
> Hey Andi,
> 	I've not been able to review the new vdso code very carefully yet, but
> I noticed one thing right off: the offset calculation is not masked, so
> its possible w/ counters less then 64bits wide to have wrapping issues.

Here's another minor cleanup. Looks like wall_time_nsec is being set
twice.

diff --git a/arch/x86_64/kernel/vsyscall.c b/arch/x86_64/kernel/vsyscall.c
index 06c3494..fc62608 100644
--- a/arch/x86_64/kernel/vsyscall.c
+++ b/arch/x86_64/kernel/vsyscall.c
@@ -80,7 +80,6 @@ void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
 	vsyscall_gtod_data.wall_time_sec = wall_time->tv_sec;
 	vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
 	vsyscall_gtod_data.sys_tz = sys_tz;
-	vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
 	vsyscall_gtod_data.wall_to_monotonic = wall_to_monotonic;
 	write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
 }


Also, is there a reason why with the new __vdso_gettimeofday
implementation, the old do_vgettimeofday has not been removed?

thanks
-john


-
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