linux-kernel - Re: Warning on boot on SAMA5D2 with Linux 4.11-rc1

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Date:   Tue, 7 Mar 2017 16:05:10 +0100
From:   Romain Izard <romain.izard.pro@...il.com>
To:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        David Engraf <david.engraf@...go.com>
Subject: Re: Warning on boot on SAMA5D2 with Linux 4.11-rc1

2017-03-06 12:28 GMT+01:00 Romain Izard <romain.izard.pro@...il.com>:
>
> While looking for another issue, I tried Linux 4.11-rc1 on a SAMA5D2 Xplained
> board. The boot log contains the following warning:
>
> [    0.100000] ------------[ cut here ]------------
> [    0.100000] WARNING: CPU: 0 PID: 1 at
> ../kernel/time/sched_clock.c:180 sched_clock_register+0x44/0x1e4
> [    0.100000] CPU: 0 PID: 1 Comm: swapper Not tainted 4.11.0-rc1+ #3
> [    0.100000] Hardware name: Atmel SAMA5
> [    0.100000] [<c010c494>] (unwind_backtrace) from [<c010a558>]
> (show_stack+0x10/0x14)
> [    0.100000] [<c010a558>] (show_stack) from [<c0115654>] (__warn+0xe0/0xf8)
> [    0.100000] [<c0115654>] (__warn) from [<c011571c>]
> (warn_slowpath_null+0x20/0x28)
> [    0.100000] [<c011571c>] (warn_slowpath_null) from [<c090b0d0>]
> (sched_clock_register+0x44/0x1e4)
> [    0.100000] [<c090b0d0>] (sched_clock_register) from [<c091fb98>]
> (tcb_clksrc_init+0x1ac/0x360)
> [    0.100000] [<c091fb98>] (tcb_clksrc_init) from [<c0900d8c>]
> (do_one_initcall+0xb4/0x15c)
> [    0.100000] [<c0900d8c>] (do_one_initcall) from [<c0900f68>]
> (kernel_init_freeable+0x134/0x1c4)
> [    0.100000] [<c0900f68>] (kernel_init_freeable) from [<c06bfc64>]
> (kernel_init+0x8/0x10c)
> [    0.100000] [<c06bfc64>] (kernel_init) from [<c0107318>]
> (ret_from_fork+0x14/0x3c)
> [    0.100000] ---[ end trace 7ce9be9d7cf6f800 ]---
> [    0.100012] sched_clock: 32 bits at 10MHz, resolution 96ns, wraps
> every 206986376143ns
>
> This is related to the following commit:
> 7b9f1d16e6d1 clocksource/drivers/tcb_clksrc: Use 32 bit tcb as sched_clock
>
> When we call sched_clock_register from tcb_clksrc_init from
> arch_initcall, we are too late as sched expects all the candidates for
> its clock to be registered before interrupts are enabled. This warning
> does not prevent the tcb clock from being used.
>

After some more use with 4.11-rc1, I also noticed that the timestamp for
printk rolls over to 0 after only 413s. Reverting the aforementioned commit
fixes it.

-- 
Romain Izard