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Date:   Fri, 15 Nov 2019 01:01:27 +0200
From:   Abel Vesa <abelvesa@linux.com>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     y2038@lists.linaro.org, John Stultz <john.stultz@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org, Stephen Boyd <sboyd@kernel.org>,
        David Howells <dhowells@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Deepa Dinamani <deepa.kernel@gmail.com>,
        Christian Brauner <christian@brauner.io>,
        Jens Axboe <axboe@kernel.dk>, Ingo Molnar <mingo@kernel.org>,
        Corey Minyard <cminyard@mvista.com>,
        zhengbin <zhengbin13@huawei.com>,
        Li RongQing <lirongqing@baidu.com>, linux-api@vger.kernel.org
Subject: Re: [PATCH 17/23] y2038: time: avoid timespec usage in settimeofday()
Message-ID: <20191114230127.GA3580@ryzen.lan>
References: <20191108210236.1296047-1-arnd@arndb.de>
 <20191108211323.1806194-8-arnd@arndb.de>
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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 get the following rcu stalls due to this patch on riscv64 (on qemu):

	[root@riscv ~]# 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@riscv ~]# [  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
	[  451.556189] rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 3-... } 100725 jiffies s: 53 root: 0x8/.
	[  451.558689] rcu: blocking rcu_node structures:
	[  451.559501] Task dump for CPU 3:
	[  451.560518] rdate           R  running task        0   254      1 0x00000008
	[  451.561396] Call Trace:
	[  451.561675] [<ffffffe00060ed48>] __schedule+0x158/0x36a
	[  483.147733] rcu: INFO: rcu_sched self-detected stall on CPU
	[  483.148723] rcu:     3-....: (115448 ticks this GP) idle=482/1/0x4000000000000002 softirq=3322/3322 fqs=56510 
	[  483.150220]  (t=115521 jiffies g=4985 q=8400)
	[  483.150885] Task dump for CPU 3:
	[  483.151392] rdate           R  running task        0   254      1 0x00000008
	[  483.152321] Call Trace:
	[  483.152755] [<ffffffe000037954>] walk_stackframe+0x0/0xa6
	[  483.153600] [<ffffffe000037aba>] show_stack+0x2a/0x34
	[  483.154428] [<ffffffe0000569c8>] sched_show_task+0xf0/0x116
	[  483.155325] [<ffffffe00005b502>] dump_cpu_task+0x3e/0x48
	[  483.156199] [<ffffffe000084e5e>] rcu_dump_cpu_stacks+0x7c/0xb4
	[  483.157163] [<ffffffe0000842f6>] rcu_sched_clock_irq+0x3d6/0x582
	[  483.158166] [<ffffffe0000897b4>] update_process_times+0x1e/0x42
	[  483.159257] [<ffffffe000093a34>] tick_sched_handle.isra.0+0x2a/0x3a
	[  483.160240] [<ffffffe000093ce8>] tick_sched_timer+0x4e/0x92
	[  483.160992] [<ffffffe000089eb6>] __hrtimer_run_queues+0xae/0x108
	[  483.161881] [<ffffffe00008a5ac>] hrtimer_interrupt+0xca/0x1d4
	[  483.162778] [<ffffffe0004de564>] riscv_timer_interrupt+0x32/0x3a
	[  483.163542] [<ffffffe000612ad4>] do_IRQ+0xa4/0xb8
	[  483.164241] [<ffffffe000036814>] ret_from_exception+0x0/0xc
	[  483.165108] [<ffffffe000036814>] ret_from_exception+0x0/0xc
	[  515.044254] rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 3-... } 116597 jiffies s: 53 root: 0x8/.
	[  515.046221] rcu: blocking rcu_node structures:
	[  515.046799] Task dump for CPU 3:
	[  515.047180] rdate           R  running task        0   254      1 0x00000008
	[  515.048476] Call Trace:
	[  515.048895] [<ffffffe00060ed48>] __schedule+0x158/0x36a

I will dig up some more into this tomorrow since it's way past by midnight here.

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  include/linux/syscalls.h |  2 +-
>  kernel/time/time.c       | 20 +++++++++-----------
>  2 files changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index e665920fa359..d0391cc2dae9 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -734,7 +734,7 @@ asmlinkage long sys_getcpu(unsigned __user *cpu, unsigned __user *node, struct g
>  /* kernel/time.c */
>  asmlinkage long sys_gettimeofday(struct __kernel_old_timeval __user *tv,
>  				struct timezone __user *tz);
> -asmlinkage long sys_settimeofday(struct timeval __user *tv,
> +asmlinkage long sys_settimeofday(struct __kernel_old_timeval __user *tv,
>  				struct timezone __user *tz);
>  asmlinkage long sys_adjtimex(struct __kernel_timex __user *txc_p);
>  asmlinkage long sys_adjtimex_time32(struct old_timex32 __user *txc_p);
> diff --git a/kernel/time/time.c b/kernel/time/time.c
> index bc114f0be8f1..6bfbe640fd3b 100644
> --- a/kernel/time/time.c
> +++ b/kernel/time/time.c
> @@ -196,22 +196,21 @@ int do_sys_settimeofday64(const struct timespec64 *tv, const struct timezone *tz
>  	return 0;
>  }
>  
> -SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
> +SYSCALL_DEFINE2(settimeofday, struct __kernel_old_timeval __user *, tv,
>  		struct timezone __user *, tz)
>  {
>  	struct timespec64 new_ts;
> -	struct timeval user_tv;
>  	struct timezone new_tz;
>  
>  	if (tv) {
> -		if (copy_from_user(&user_tv, tv, sizeof(*tv)))
> +		if (get_user(new_ts.tv_sec, &tv->tv_sec) ||
> +		    get_user(new_ts.tv_nsec, &tv->tv_usec))
>  			return -EFAULT;
>  
> -		if (!timeval_valid(&user_tv))
> +		if (tv->tv_usec > USEC_PER_SEC)
>  			return -EINVAL;
>  
> -		new_ts.tv_sec = user_tv.tv_sec;
> -		new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
> +		new_ts.tv_nsec *= NSEC_PER_USEC;
>  	}
>  	if (tz) {
>  		if (copy_from_user(&new_tz, tz, sizeof(*tz)))
> @@ -245,18 +244,17 @@ COMPAT_SYSCALL_DEFINE2(settimeofday, struct old_timeval32 __user *, tv,
>  		       struct timezone __user *, tz)
>  {
>  	struct timespec64 new_ts;
> -	struct timeval user_tv;
>  	struct timezone new_tz;
>  
>  	if (tv) {
> -		if (compat_get_timeval(&user_tv, tv))
> +		if (get_user(new_ts.tv_sec, &tv->tv_sec) ||
> +		    get_user(new_ts.tv_nsec, &tv->tv_usec))
>  			return -EFAULT;
>  
> -		if (!timeval_valid(&user_tv))
> +		if (new_ts.tv_nsec > USEC_PER_SEC)
>  			return -EINVAL;
>  
> -		new_ts.tv_sec = user_tv.tv_sec;
> -		new_ts.tv_nsec = user_tv.tv_usec * NSEC_PER_USEC;
> +		new_ts.tv_nsec *= NSEC_PER_USEC;
>  	}
>  	if (tz) {
>  		if (copy_from_user(&new_tz, tz, sizeof(*tz)))
> -- 
> 2.20.0
>