Re: [PATCH rcu 03/12] srcu: Renaming in preparation for additional reader flavor

[Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>]

On 10/14/2024 10:22 PM, Paul E. McKenney wrote:
> On Mon, Oct 14, 2024 at 02:40:35PM +0530, Neeraj Upadhyay wrote:
>> On 10/9/2024 11:37 PM, Paul E. McKenney wrote:
>>> Currently, there are only two flavors of readers, normal and NMI-safe.
>>> A number of fields, functions, and types reflect this restriction.
>>> This renaming-only commit prepares for the addition of light-weight
>>> (as in memory-barrier-free) readers.  OK, OK, there is also a drive-by
>>> white-space fixeup!
>>>
>>> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>>> Cc: Alexei Starovoitov <ast@kernel.org>
>>> Cc: Andrii Nakryiko <andrii@kernel.org>
>>> Cc: Peter Zijlstra <peterz@infradead.org>
>>> Cc: Kent Overstreet <kent.overstreet@linux.dev>
>>> Cc: <bpf@vger.kernel.org>
>>> ---
>>>  include/linux/srcu.h     | 21 ++++++++++-----------
>>>  include/linux/srcutree.h |  2 +-
>>>  kernel/rcu/srcutree.c    | 22 +++++++++++-----------
>>>  3 files changed, 22 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
>>> index 835bbb2d1f88a..06728ef6f32a4 100644
>>> --- a/include/linux/srcu.h
>>> +++ b/include/linux/srcu.h
>>> @@ -181,10 +181,9 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
>>>  #define SRCU_NMI_SAFE		0x2
>>>  
>>>  #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)
>>> -void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe);
>>> +void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
>>>  #else
>>> -static inline void srcu_check_nmi_safety(struct srcu_struct *ssp,
>>> -					 bool nmi_safe) { }
>>> +static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) { }
>>>  #endif
>>>  
>>>  
>>> @@ -245,7 +244,7 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
>>>  {
>>>  	int retval;
>>>  
>>> -	srcu_check_nmi_safety(ssp, false);
>>> +	srcu_check_read_flavor(ssp, false);
>>
>> As srcu_check_read_flavor() takes an "int" now, passing a macro for the type of reader would
>> be better here?
> 
> Agreed, and a later commit does introduce macros.
> 
>>>  	retval = __srcu_read_lock(ssp);
>>>  	srcu_lock_acquire(&ssp->dep_map);
>>>  	return retval;
>>> @@ -262,7 +261,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp
>>>  {
>>>  	int retval;
>>>  
>>> -	srcu_check_nmi_safety(ssp, true);
>>> +	srcu_check_read_flavor(ssp, true);
>>>  	retval = __srcu_read_lock_nmisafe(ssp);
>>>  	rcu_try_lock_acquire(&ssp->dep_map);
>>>  	return retval;
>>> @@ -274,7 +273,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
>>>  {
>>>  	int retval;
>>>  
>>> -	srcu_check_nmi_safety(ssp, false);
>>> +	srcu_check_read_flavor(ssp, false);
>>>  	retval = __srcu_read_lock(ssp);
>>>  	return retval;
>>>  }
>>> @@ -303,7 +302,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
>>>  static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
>>>  {
>>>  	WARN_ON_ONCE(in_nmi());
>>> -	srcu_check_nmi_safety(ssp, false);
>>> +	srcu_check_read_flavor(ssp, false);
>>>  	return __srcu_read_lock(ssp);
>>>  }
>>>  
>>> @@ -318,7 +317,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
>>>  	__releases(ssp)
>>>  {
>>>  	WARN_ON_ONCE(idx & ~0x1);
>>> -	srcu_check_nmi_safety(ssp, false);
>>> +	srcu_check_read_flavor(ssp, false);
>>>  	srcu_lock_release(&ssp->dep_map);
>>>  	__srcu_read_unlock(ssp, idx);
>>>  }
>>> @@ -334,7 +333,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
>>>  	__releases(ssp)
>>>  {
>>>  	WARN_ON_ONCE(idx & ~0x1);
>>> -	srcu_check_nmi_safety(ssp, true);
>>> +	srcu_check_read_flavor(ssp, true);
>>>  	rcu_lock_release(&ssp->dep_map);
>>>  	__srcu_read_unlock_nmisafe(ssp, idx);
>>>  }
>>> @@ -343,7 +342,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
>>>  static inline notrace void
>>>  srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
>>>  {
>>> -	srcu_check_nmi_safety(ssp, false);
>>> +	srcu_check_read_flavor(ssp, false);
>>>  	__srcu_read_unlock(ssp, idx);
>>>  }
>>>  
>>> @@ -360,7 +359,7 @@ static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
>>>  {
>>>  	WARN_ON_ONCE(idx & ~0x1);
>>>  	WARN_ON_ONCE(in_nmi());
>>> -	srcu_check_nmi_safety(ssp, false);
>>> +	srcu_check_read_flavor(ssp, false);
>>>  	__srcu_read_unlock(ssp, idx);
>>>  }
>>>  
>>> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
>>> index ed57598394de3..ab7d8d215b84b 100644
>>> --- a/include/linux/srcutree.h
>>> +++ b/include/linux/srcutree.h
>>> @@ -25,7 +25,7 @@ struct srcu_data {
>>>  	/* Read-side state. */
>>>  	atomic_long_t srcu_lock_count[2];	/* Locks per CPU. */
>>>  	atomic_long_t srcu_unlock_count[2];	/* Unlocks per CPU. */
>>> -	int srcu_nmi_safety;			/* NMI-safe srcu_struct structure? */
>>> +	int srcu_reader_flavor;			/* Reader flavor for srcu_struct structure? */
>>
>> This is a mask for the reader flavor, so s/srcu_reader_flavor/srcu_reader_flavor_mask ?
> 
> Yes, it is a mask, but one that should only ever have a single bit set.
> So calling it a mask might or might not be a service to the reader.
> 

Ok. The usage of reader_flavor as a shifted val here and without
shift as arg of srcu_check_read_flavor() was a bit confusing.


- Neeraj

...

>>>  
>>>  #ifdef CONFIG_PROVE_RCU
>>>  /*
>>> - * Check for consistent NMI safety.
>>> + * Check for consistent reader flavor.
>>>   */
>>> -void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe)
>>> +void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
>>>  {
>>> -	int nmi_safe_mask = 1 << nmi_safe;
>>> -	int old_nmi_safe_mask;
>>> +	int reader_flavor_mask = 1 << read_flavor;
>>> +	int old_reader_flavor_mask;
>>>  	struct srcu_data *sdp;
>>>  
>>>  	/* NMI-unsafe use in NMI is a bad sign */
>>> -	WARN_ON_ONCE(!nmi_safe && in_nmi());
>>> +	WARN_ON_ONCE(!read_flavor && in_nmi());
>>>  	sdp = raw_cpu_ptr(ssp->sda);
>>> -	old_nmi_safe_mask = READ_ONCE(sdp->srcu_nmi_safety);
>>> -	if (!old_nmi_safe_mask) {
>>> -		WRITE_ONCE(sdp->srcu_nmi_safety, nmi_safe_mask);
>>> +	old_reader_flavor_mask = READ_ONCE(sdp->srcu_reader_flavor);
>>> +	if (!old_reader_flavor_mask) {
>>> +		WRITE_ONCE(sdp->srcu_reader_flavor, reader_flavor_mask);
>>>  		return;
>>>  	}
>>> -	WARN_ONCE(old_nmi_safe_mask != nmi_safe_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_nmi_safe_mask, nmi_safe_mask);
>>> +	WARN_ONCE(old_reader_flavor_mask != reader_flavor_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_reader_flavor_mask, reader_flavor_mask);
>>>  }
>>> -EXPORT_SYMBOL_GPL(srcu_check_nmi_safety);
>>> +EXPORT_SYMBOL_GPL(srcu_check_read_flavor);
>>>  #endif /* CONFIG_PROVE_RCU */
>>>  
>>>  /*
>>