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sched/clock: Provide local_clock_noinstr()

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Now that all ARCH_WANTS_NO_INSTR architectures (arm64, loongarch,
s390, x86) provide sched_clock_noinstr(), use this to provide
local_clock_noinstr().

This local_clock_noinstr() will be safe to use from noinstr code with
the assumption that any such noinstr code is non-preemptible (it had
better be, entry code will have IRQs disabled while __cpuidle must
have preemption disabled).

Specifically, preempt_enable_notrace(), a common part of many a
sched_clock() implementation calls out to schedule() -- even though,
per the above, it will never trigger -- which frustrates noinstr
validation.

  vmlinux.o: warning: objtool: local_clock+0xb5: call to preempt_schedule_notrace_thunk() leaves .noinstr.text section

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>  # Hyper-V
Link: https://lore.kernel.org/r/20230519102715.978624636@infradead.org
This commit is contained in:
Peter Zijlstra
2023-05-19 12:21:10 +02:00
parent 5c5e9a2b25
commit fb7d4948c4
2 changed files with 29 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
kernel/sched/clock.c
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@@ -266,7 +266,7 @@ static __always_inline u64 sched_clock_local(struct sched_clock_data *scd)
s64 delta;
again:
now = sched_clock();
now = sched_clock_noinstr();
delta = now - scd->tick_raw;
if (unlikely(delta < 0))
delta = 0;
@@ -293,22 +293,29 @@ static __always_inline u64 sched_clock_local(struct sched_clock_data *scd)
return clock;
}
noinstr u64 local_clock(void)
noinstr u64 local_clock_noinstr(void)
{
u64 clock;
if (static_branch_likely(&__sched_clock_stable))
return sched_clock() + __sched_clock_offset;
return sched_clock_noinstr() + __sched_clock_offset;
if (!static_branch_likely(&sched_clock_running))
return sched_clock();
return sched_clock_noinstr();
preempt_disable_notrace();
clock = sched_clock_local(this_scd());
preempt_enable_notrace();
return clock;
}
u64 local_clock(void)
{
u64 now;
preempt_disable_notrace();
now = local_clock_noinstr();
preempt_enable_notrace();
return now;
}
EXPORT_SYMBOL_GPL(local_clock);
static notrace u64 sched_clock_remote(struct sched_clock_data *scd)