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

From: Abel Vesa
Date: Thu Nov 14 2019 - 18:01:41 EST

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@xxxxxxxx>
> ---
> 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
>