* [PATCH] blktrace: reword comment about time overflow
@ 2016-06-20 20:00 Arnd Bergmann
2016-06-20 20:36 ` Jeff Moyer
0 siblings, 1 reply; 2+ messages in thread
From: Arnd Bergmann @ 2016-06-20 20:00 UTC (permalink / raw)
To: Jens Axboe
Cc: y2038, Arnd Bergmann, Jeff Moyer, Steven Rostedt, Ingo Molnar,
Hannes Reinecke, Mike Christie, Shaohua Li, linux-block,
linux-kernel
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>
---
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;
--
2.9.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] blktrace: reword comment about time overflow
2016-06-20 20:00 [PATCH] blktrace: reword comment about time overflow Arnd Bergmann
@ 2016-06-20 20:36 ` Jeff Moyer
0 siblings, 0 replies; 2+ messages in thread
From: Jeff Moyer @ 2016-06-20 20:36 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Jens Axboe, y2038, Steven Rostedt, Ingo Molnar, Hannes Reinecke,
Mike Christie, Shaohua Li, linux-block, linux-kernel
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;
^ permalink raw reply [flat|nested] 2+ messages in thread
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