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cpuidle: Add comments about noinstr/__cpuidle usage

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Add a few words on noinstr / __cpuidle usage.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230112195542.397238052@infradead.org
This commit is contained in:
Peter Zijlstra 2023-01-12 20:44:04 +01:00 committed by Ingo Molnar
parent 26388a7c35
commit 0e985e9d22
2 changed files with 22 additions and 0 deletions
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12
drivers/cpuidle/cpuidle.c
View File

@ -252,6 +252,18 @@ noinstr int cpuidle_enter_state(struct cpuidle_device *dev,
instrumentation_begin();
}
/*
* NOTE!!
*
* For cpuidle_state::enter() methods that do *NOT* set
* CPUIDLE_FLAG_RCU_IDLE RCU will be disabled here and these functions
* must be marked either noinstr or __cpuidle.
*
* For cpuidle_state::enter() methods that *DO* set
* CPUIDLE_FLAG_RCU_IDLE this isn't required, but they must mark the
* function calling ct_cpuidle_enter() as noinstr/__cpuidle and all
* functions called within the RCU-idle region.
*/
entered_state = target_state->enter(dev, drv, index);
if (WARN_ONCE(!irqs_disabled(), "%ps leaked IRQ state", target_state->enter))

10
include/linux/compiler_types.h
View File

@ -239,6 +239,16 @@ struct ftrace_likely_data {
#define noinstr __noinstr_section(".noinstr.text")
/*
* The __cpuidle section is used twofold:
*
* 1) the original use -- identifying if a CPU is 'stuck' in idle state based
* on it's instruction pointer. See cpu_in_idle().
*
* 2) supressing instrumentation around where cpuidle disables RCU; where the
* function isn't strictly required for #1, this is interchangeable with
* noinstr.
*/
#define __cpuidle __noinstr_section(".cpuidle.text")
#endif /* __KERNEL__ */