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Subject[PATCH v3] sched/cputime: Fix using smp_processor_id() in preemptible
Date
From: Wanpeng Li <wanpeng.li@hotmail.com>

BUG: using smp_processor_id() in preemptible [00000000] code: 99-trinity/181
caller is debug_smp_processor_id+0x17/0x19
CPU: 0 PID: 181 Comm: 99-trinity Not tainted 4.12.0-01059-g2a42eb9 #1
Call Trace:
dump_stack+0x82/0xb8
check_preemption_disabled+0xd1/0xe3
debug_smp_processor_id+0x17/0x19
vtime_delta+0xd/0x2c
task_cputime+0x89/0xdb
thread_group_cputime+0x11b/0x1ed
thread_group_cputime_adjusted+0x1f/0x47
wait_consider_task+0x2a9/0xaf9
? lock_acquire+0x97/0xa4
do_wait+0xdf/0x1f4
SYSC_wait4+0x8e/0xb5
? list_add+0x34/0x34
SyS_wait4+0x9/0xb
do_syscall_64+0x70/0x82
entry_SYSCALL64_slow_path+0x25/0x25

As Frederic pointed out:

| Although those sched_clock_cpu() things seem to only matter when the
| sched_clock() is unstable. And that stability is a condition for nohz_full
| to work anyway. So probably sched_clock() alone would be enough.

This patch fixes it by replacing sched_clock_cpu() by sched_clock() to
avoid to call smp_processor_id() in preemptible context.

Reported-by: Xiaolong Ye <xiaolong.ye@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
kernel/sched/cputime.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 6e3ea4a..14d2dbf 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -683,7 +683,7 @@ static u64 vtime_delta(struct vtime *vtime)
{
unsigned long long clock;

- clock = sched_clock_cpu(smp_processor_id());
+ clock = sched_clock();
if (clock < vtime->starttime)
return 0;

@@ -814,7 +814,7 @@ void arch_vtime_task_switch(struct task_struct *prev)

write_seqcount_begin(&vtime->seqcount);
vtime->state = VTIME_SYS;
- vtime->starttime = sched_clock_cpu(smp_processor_id());
+ vtime->starttime = sched_clock();
write_seqcount_end(&vtime->seqcount);
}

@@ -826,7 +826,7 @@ void vtime_init_idle(struct task_struct *t, int cpu)
local_irq_save(flags);
write_seqcount_begin(&vtime->seqcount);
vtime->state = VTIME_SYS;
- vtime->starttime = sched_clock_cpu(cpu);
+ vtime->starttime = sched_clock();
write_seqcount_end(&vtime->seqcount);
local_irq_restore(flags);
}
--
2.7.4
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