linux-kernel - Re: [PATCH v2] pstore/ram: no timekeeping calls when unavailable

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Date:	Fri, 09 Nov 2012 16:56:30 -0800
From:	John Stultz <johnstul@...ibm.com>
To:	Kees Cook <keescook@...omium.org>
CC:	linux-kernel@...r.kernel.org,
	Anton Vorontsov <cbouatmailru@...il.com>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] pstore/ram: no timekeeping calls when unavailable

On 11/05/2012 02:00 PM, Kees Cook wrote:
> We must not call timekeeping functions unless they are available. If we dump
> before they have resumed, avoid a WARN_ON by setting the timestamp to 0.
>
> Since the "ram" pstore driver can be a module, we must have
> timekeeping_suspended exported.
>
> Reported-by: Doug Anderson <dianders@...omium.org>
> Cc: Anton Vorontsov <cbouatmailru@...il.com>
> Cc: John Stultz <johnstul@...ibm.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v2:
>   - export needed for timekeeping_suspended (thanks to Fengguang Wu).
> ---
>   fs/pstore/ram.c           |    8 +++++++-
>   kernel/time/timekeeping.c |    1 +
>   2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index 1a4f6da..6d014e0 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -171,7 +171,13 @@ static size_t ramoops_write_kmsg_hdr(struct persistent_ram_zone *prz)
>   	struct timeval timestamp;
>   	size_t len;
>
> -	do_gettimeofday(&timestamp);
> +	/* Handle dumping before timekeeping has resumed. */
> +	if (unlikely(timekeeping_suspended)) {
> +		timestamp.tv_sec = 0;
> +		timestamp.tv_usec = 0;
> +	} else
> +		do_gettimeofday(&timestamp);
> +
Would nulling out the timestamp be better done in do_gettimeofday()?  
That way we don't have to export timekeeping internals and users would 
get something more sane for this corner case.

thanks
-john


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