lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Wed, 11 Sep 2013 09:43:28 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Richard Cochran <richardcochran@...il.com>,
	Prarit Bhargava <prarit@...hat.com>, lttng-dev@...ts.lttng.org,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC PATCH lttng-modules] Fix: use timekeeping_is_busy() to fix
 ktime_get() hard lockup

On 09/11/2013 08:12 AM, Mathieu Desnoyers wrote:
> LTTng uses ktime to have the same time-base across kernel and
> user-space, so traces gathered from LTTng-modules and LTTng-UST can be
> correlated. We plan on using ktime until a fast, scalable, and
> fine-grained time-source for tracing that can be used across kernel and
> user-space, and which does not rely on read seqlock for kernel-level
> synchronization, makes its way into the kernel.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Richard Cochran <richardcochran@...il.com>
> Cc: Prarit Bhargava <prarit@...hat.com>
> Cc: John Stultz <john.stultz@...aro.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> ---
> diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
> index bced61c..2f9df7a 100644
> --- a/wrapper/trace-clock.h
> +++ b/wrapper/trace-clock.h
> @@ -32,6 +32,7 @@
>  #include <linux/ktime.h>
>  #include <linux/time.h>
>  #include <linux/hrtimer.h>
> +#include <linux/version.h>
>  #include "random.h"
>  
>  static inline u64 trace_clock_monotonic_wrapper(void)
> @@ -45,6 +46,10 @@ static inline u64 trace_clock_monotonic_wrapper(void)
>  	if (in_nmi())
>  		return (u64) -EIO;
>  
> +#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,10,0))
> +	if (timekeeping_is_busy())
> +		return (u64) -EIO;
> +#endif
>  	ktime = ktime_get();
>  	return ktime_to_ns(ktime);
>  }


I guess the other question here is should this functionality be pushed
down into the timekeeping accessors themselves?

I know any extra checks would probably be considered overhead in some
uses, but if we do the check only when we hit contention then it might
not be so bad.

thanks
-john



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists