Re: [PATCH rcu 05/12] srcu: Standardize srcu_data pointers to "sdp" and similar

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

On 10/9/2024 11:37 PM, Paul E. McKenney wrote:
> This commit changes a few "cpuc" variables to "sdp" to align wiht usage
> elsewhere.
> 

s/wiht/with/

This commit is doing a lot more than renaming "cpuc".



- Neeraj

> 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     | 35 ++++++++++++++++++----------------
>  include/linux/srcutree.h |  4 ++++
>  kernel/rcu/srcutree.c    | 41 ++++++++++++++++++++--------------------
>  3 files changed, 44 insertions(+), 36 deletions(-)
> 
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index 06728ef6f32a4..84daaa33ea0ab 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -176,10 +176,6 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
>  
>  #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>  
> -#define SRCU_NMI_UNKNOWN	0x0
> -#define SRCU_NMI_UNSAFE		0x1
> -#define SRCU_NMI_SAFE		0x2
> -
>  #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)
>  void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
>  #else
> @@ -235,16 +231,19 @@ static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flav
>   * a mutex that is held elsewhere while calling synchronize_srcu() or
>   * synchronize_srcu_expedited().
>   *
> - * Note that srcu_read_lock() and the matching srcu_read_unlock() must
> - * occur in the same context, for example, it is illegal to invoke
> - * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
> - * was invoked in process context.
> + * The return value from srcu_read_lock() must be passed unaltered
> + * to the matching srcu_read_unlock().  Note that srcu_read_lock() and
> + * the matching srcu_read_unlock() must occur in the same context, for
> + * example, it is illegal to invoke srcu_read_unlock() in an irq handler
> + * if the matching srcu_read_lock() was invoked in process context.  Or,
> + * for that matter to invoke srcu_read_unlock() from one task and the
> + * matching srcu_read_lock() from another.
>   */
>  static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
>  {
>  	int retval;
>  
> -	srcu_check_read_flavor(ssp, false);
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
>  	retval = __srcu_read_lock(ssp);
>  	srcu_lock_acquire(&ssp->dep_map);
>  	return retval;
> @@ -256,12 +255,16 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
>   *
>   * Enter an SRCU read-side critical section, but in an NMI-safe manner.
>   * See srcu_read_lock() for more information.
> + *
> + * If srcu_read_lock_nmisafe() is ever used on an srcu_struct structure,
> + * then none of the other flavors may be used, whether before, during,
> + * or after.
>   */
>  static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
>  {
>  	int retval;
>  
> -	srcu_check_read_flavor(ssp, true);
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
>  	retval = __srcu_read_lock_nmisafe(ssp);
>  	rcu_try_lock_acquire(&ssp->dep_map);
>  	return retval;
> @@ -273,7 +276,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
>  {
>  	int retval;
>  
> -	srcu_check_read_flavor(ssp, false);
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
>  	retval = __srcu_read_lock(ssp);
>  	return retval;
>  }
> @@ -302,7 +305,7 @@ 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_read_flavor(ssp, false);
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
>  	return __srcu_read_lock(ssp);
>  }
>  
> @@ -317,7 +320,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
>  	__releases(ssp)
>  {
>  	WARN_ON_ONCE(idx & ~0x1);
> -	srcu_check_read_flavor(ssp, false);
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
>  	srcu_lock_release(&ssp->dep_map);
>  	__srcu_read_unlock(ssp, idx);
>  }
> @@ -333,7 +336,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
>  	__releases(ssp)
>  {
>  	WARN_ON_ONCE(idx & ~0x1);
> -	srcu_check_read_flavor(ssp, true);
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
>  	rcu_lock_release(&ssp->dep_map);
>  	__srcu_read_unlock_nmisafe(ssp, idx);
>  }
> @@ -342,7 +345,7 @@ 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_read_flavor(ssp, false);
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
>  	__srcu_read_unlock(ssp, idx);
>  }
>  
> @@ -359,7 +362,7 @@ static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
>  {
>  	WARN_ON_ONCE(idx & ~0x1);
>  	WARN_ON_ONCE(in_nmi());
> -	srcu_check_read_flavor(ssp, false);
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
>  	__srcu_read_unlock(ssp, idx);
>  }
>  
> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
> index ab7d8d215b84b..79ad809c7f035 100644
> --- a/include/linux/srcutree.h
> +++ b/include/linux/srcutree.h
> @@ -43,6 +43,10 @@ struct srcu_data {
>  	struct srcu_struct *ssp;
>  };
>  
> +/* Values for ->srcu_reader_flavor. */
> +#define SRCU_READ_FLAVOR_NORMAL	0x1		// srcu_read_lock().
> +#define SRCU_READ_FLAVOR_NMI	0x2		// srcu_read_lock_nmisafe().
> +
>  /*
>   * Node in SRCU combining tree, similar in function to rcu_data.
>   */
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index abe55777c4335..4c51be484b48a 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -438,9 +438,9 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx)
>  	unsigned long sum = 0;
>  
>  	for_each_possible_cpu(cpu) {
> -		struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
> +		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
>  
> -		sum += atomic_long_read(&cpuc->srcu_lock_count[idx]);
> +		sum += atomic_long_read(&sdp->srcu_lock_count[idx]);
>  	}
>  	return sum;
>  }
> @@ -456,14 +456,14 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
>  	unsigned long sum = 0;
>  
>  	for_each_possible_cpu(cpu) {
> -		struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
> +		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
>  
> -		sum += atomic_long_read(&cpuc->srcu_unlock_count[idx]);
> +		sum += atomic_long_read(&sdp->srcu_unlock_count[idx]);
>  		if (IS_ENABLED(CONFIG_PROVE_RCU))
> -			mask = mask | READ_ONCE(cpuc->srcu_reader_flavor);
> +			mask = mask | READ_ONCE(sdp->srcu_reader_flavor);
>  	}
>  	WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)),
> -		  "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp);
> +		  "Mixed reader flavors for srcu_struct at %ps.\n", ssp);
>  	return sum;
>  }
>  
> @@ -564,12 +564,12 @@ static bool srcu_readers_active(struct srcu_struct *ssp)
>  	unsigned long sum = 0;
>  
>  	for_each_possible_cpu(cpu) {
> -		struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
> +		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
>  
> -		sum += atomic_long_read(&cpuc->srcu_lock_count[0]);
> -		sum += atomic_long_read(&cpuc->srcu_lock_count[1]);
> -		sum -= atomic_long_read(&cpuc->srcu_unlock_count[0]);
> -		sum -= atomic_long_read(&cpuc->srcu_unlock_count[1]);
> +		sum += atomic_long_read(&sdp->srcu_lock_count[0]);
> +		sum += atomic_long_read(&sdp->srcu_lock_count[1]);
> +		sum -= atomic_long_read(&sdp->srcu_unlock_count[0]);
> +		sum -= atomic_long_read(&sdp->srcu_unlock_count[1]);
>  	}
>  	return sum;
>  }
> @@ -703,20 +703,21 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
>   */
>  void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
>  {
> -	int reader_flavor_mask = 1 << read_flavor;
> -	int old_reader_flavor_mask;
> +	int old_read_flavor;
>  	struct srcu_data *sdp;
>  
> -	/* NMI-unsafe use in NMI is a bad sign */
> -	WARN_ON_ONCE(!read_flavor && in_nmi());
> +	/* NMI-unsafe use in NMI is a bad sign, as is multi-bit read_flavor values. */
> +	WARN_ON_ONCE((read_flavor != SRCU_READ_FLAVOR_NMI) && in_nmi());
> +	WARN_ON_ONCE(read_flavor & (read_flavor - 1));
> +
>  	sdp = raw_cpu_ptr(ssp->sda);
> -	old_reader_flavor_mask = READ_ONCE(sdp->srcu_reader_flavor);
> -	if (!old_reader_flavor_mask) {
> -		old_reader_flavor_mask = cmpxchg(&sdp->srcu_reader_flavor, 0, reader_flavor_mask);
> -		if (!old_reader_flavor_mask)
> +	old_read_flavor = READ_ONCE(sdp->srcu_reader_flavor);
> +	if (!old_read_flavor) {
> +		old_read_flavor = cmpxchg(&sdp->srcu_reader_flavor, 0, read_flavor);
> +		if (!old_read_flavor)
>  			return;
>  	}
> -	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);
> +	WARN_ONCE(old_read_flavor != read_flavor, "CPU %d old state %d new state %d\n", sdp->cpu, old_read_flavor, read_flavor);
>  }
>  EXPORT_SYMBOL_GPL(srcu_check_read_flavor);
>  #endif /* CONFIG_PROVE_RCU */