linux-kernel - Re: [PATCH 17/23] y2038: time: avoid timespec usage in settimeofday()

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Date:   Fri, 15 Nov 2019 08:58:38 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Abel Vesa <abelvesa@...ux.com>
Cc:     y2038 Mailman List <y2038@...ts.linaro.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Christian Brauner <christian@...uner.io>,
        Jens Axboe <axboe@...nel.dk>, Ingo Molnar <mingo@...nel.org>,
        Corey Minyard <cminyard@...sta.com>,
        zhengbin <zhengbin13@...wei.com>,
        Li RongQing <lirongqing@...du.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH 17/23] y2038: time: avoid timespec usage in settimeofday()

On Fri, Nov 15, 2019 at 12:01 AM Abel Vesa <abelvesa@...ux.com> wrote:
>
> On 19-11-08 22:12:16, Arnd Bergmann wrote:
> > The compat_get_timeval() and timeval_valid() interfaces
> > are deprecated and getting removed along with the definition
> > of struct timeval itself.
> >
> > Change the two implementations of the settimeofday()
> > system call to open-code these helpers and completely
> > avoid references to timeval.
> >

I'm not sure how we get to the RCU stall, but this is almost certainly another
symptom of a typo I had introduced in the patch, which others have also
reported. This is the the fix in today's linux-next:

--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -207,7 +207,7 @@ SYSCALL_DEFINE2(settimeofday, struct
__kernel_old_timeval __user *, tv,
                    get_user(new_ts.tv_nsec, &tv->tv_usec))
                        return -EFAULT;

-               if (tv->tv_usec > USEC_PER_SEC)
+               if (new_ts->tv_usec > USEC_PER_SEC)
                        return -EINVAL;

                new_ts.tv_nsec *= NSEC_PER_USEC;


    Arnd

> I get the following rcu stalls due to this patch on riscv64 (on qemu):
>
>         [root@...cv ~]# uname -a
>         Linux riscv 5.4.0-rc6-00018-gadde74306a4b #112 SMP Fri Nov 15 00:46:20 EET 2019 riscv64 riscv64 riscv64 GNU/Linux
>         [root@...cv ~]# [  420.135710] rcu: INFO: rcu_sched self-detected stall
>         on CPU
>         [  420.136839] rcu:     3-....: (99702 ticks this GP) idle=482/1/0x4000000000000002 softirq=3322/3322 fqs=48784
>         [  420.138917]  (t=99768 jiffies g=4985 q=8343)
>         [  420.139772] Task dump for CPU 3:
>         [  420.140236] rdate           R  running task        0   254      1 0x00000008
>         [  420.142226] Call Trace:
>         [  420.142791] [<ffffffe000037954>] walk_stackframe+0x0/0xa6
>         [  420.143911] [<ffffffe000037aba>] show_stack+0x2a/0x34
>         [  420.145010] [<ffffffe0000569c8>] sched_show_task+0xf0/0x116
>         [  420.145996] [<ffffffe00005b502>] dump_cpu_task+0x3e/0x48
>         [  420.147073] [<ffffffe000084e5e>] rcu_dump_cpu_stacks+0x7c/0xb4
>         [  420.148243] [<ffffffe0000842f6>] rcu_sched_clock_irq+0x3d6/0x582
>         [  420.149349] [<ffffffe0000897b4>] update_process_times+0x1e/0x42
>         [  420.150306] [<ffffffe000093a34>] tick_sched_handle.isra.0+0x2a/0x3a
>         [  420.150997] [<ffffffe000093ce8>] tick_sched_timer+0x4e/0x92
>         [  420.151603] [<ffffffe000089eb6>] __hrtimer_run_queues+0xae/0x108
>         [  420.152639] [<ffffffe00008a5ac>] hrtimer_interrupt+0xca/0x1d4
>         [  420.153629] [<ffffffe0004de564>] riscv_timer_interrupt+0x32/0x3a
>         [  420.154629] [<ffffffe000612ad4>] do_IRQ+0xa4/0xb8
>         [  420.155294] [<ffffffe000036814>] ret_from_exception+0x0/0xc
>         [  420.156073] [<ffffffe000036814>] ret_from_exception+0x0/0xc