Arnd Bergmann <arnd@xxxxxxxx> 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@xxxxxxxx>
> Fixes: 59a37f8baeb2 ("blktrace: avoid using timespec")
> Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Acked-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
> ---
> 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;
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