| Date | Wed, 26 Jul 2017 15:21:20 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 4.12 178/196] sched/cputime: Accumulate vtime on top of nsec clocksource |
| |
I noticed relatively late and it hadn't occured on my own testing. I can send it as a separate patch but I wanted to highlight that it would affect a 4.12.4 release.
---8<--- sched/cputime: Don't use smp_processor_id() in preemptible context
commit 0e4097c3354e2f5a5ad8affd9dc7f7f7d00bb6b9 upstream
Recent kernels trigger this warning:
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() debug_smp_processor_id() vtime_delta() task_cputime() thread_group_cputime() thread_group_cputime_adjusted() wait_consider_task() do_wait() SYSC_wait4() do_syscall_64() entry_SYSCALL64_slow_path()
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() with sched_clock() to avoid calling smp_processor_id() in a preemptible context.
Reported-by: Xiaolong Ye <xiaolong.ye@intel.com> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Luiz Capitulino <lcapitulino@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1499586028-7402-1-git-send-email-wanpeng.li@hotmail.com [ Prettified the changelog. ] Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Mel Gorman <mgorman@suse.de>
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 3dafea579263..ad275b25e3f9 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); }
|