On 10/17/2014 09:57 AM, Prarit Bhargava wrote:
> A bug report came in against an older kernel which output "backward time"
> messages and the report noted that the upstream kernel worked. After some
> investigation it turned out that one of the sockets was bad on the system
> and the "backward time" messages were caused by a real, but intermittent,
> hardware failure.
>
> Commit 09ec54429c6d10f87d1f084de53ae2c1c3a81108 ("clocksource: Move
> cycle_last validation to core code") modifies the x86 clocksource such that
> if a negative delta between two reads of time is calculated the
> clocksource_delta() code will return 0. There is no warning when this
> occurs and there really should be one in order to catch not only hardware
> issues like the issue above, but potential coding issues as the code is
> modified. This patch introduces a WARN() which will also dump a stack
> trace to the console so the exact code path can be evaluated.
>
> I tested this by booting on the broken hardware and left the system idle
> until a negative clocksource_delta() event occurred.
>
> Cc: John Stultz <john.stu...@linaro.org>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Signed-off-by: Prarit Bhargava <pra...@redhat.com>
Sorry everyone -- I accidentally sent this out. It is still untested and needs
some bake time.
Please ignore this patch.
P.
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