From: Jeff Moyer <jmoyer@redhat.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Jens Axboe <axboe@kernel.dk>,
y2038@lists.linaro.org, Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>, Hannes Reinecke <hare@suse.com>,
Mike Christie <mchristi@redhat.com>, Shaohua Li <shli@fb.com>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] blktrace: reword comment about time overflow
Date: Mon, 20 Jun 2016 16:36:58 -0400 [thread overview]
Message-ID: <x49porbr40l.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <20160620200040.2813298-1-arnd@arndb.de> (Arnd Bergmann's message of "Mon, 20 Jun 2016 22:00:12 +0200")
Arnd Bergmann <arnd@arndb.de> writes:
> Jeff Moyer looked up the blktrace source to see if an overflow might
> happen. The situation is as follows:
>
> - The time stamp is not used by the program itself, only for
> printing human-readable output.
> - We normally don't print the timestamp at all, except when an
> undocumented format option is given to blkparse.
> - The assumption is that no other program besides blktrace
> even looks at this data, but of course cannot be sure.
> - On 64-bit systems, the time gets read from the unsigned
> 32-bit kernel structure into a timespec in a way that will
> work correctly until 2106, so there is no 2038 problem.
> - On 32-bit systems that have a new (future) libc build with
> a 64-bit time_t type, it will work the same way.
> - On current 32-bit systems, the time is passed into localtime(),
> at which point the overflow happens, but those systems are
> already broken.
>
> In short, it's good enough for now, so update the comment.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Fixes: 59a37f8baeb2 ("blktrace: avoid using timespec")
> Cc: Jeff Moyer <jmoyer@redhat.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
> ---
> kernel/trace/blktrace.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index b0816e4a61a5..4a3666779589 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -131,7 +131,8 @@ static void trace_note_time(struct blk_trace *bt)
> unsigned long flags;
> u32 words[2];
>
> - /* need to check user space to see if this breaks in y2038 or y2106 */
> + /* blktrace converts this to a time_t and will overflow in
> + 2106, not in 2038 */
> ktime_get_real_ts64(&now);
> words[0] = (u32)now.tv_sec;
> words[1] = now.tv_nsec;
prev parent reply other threads:[~2016-06-20 20:48 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-20 20:00 [PATCH] blktrace: reword comment about time overflow Arnd Bergmann
2016-06-20 20:36 ` Jeff Moyer [this message]
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