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

From: Neeraj Upadhyay
Date: Tue Oct 15 2024 - 01:10:54 EST

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On 10/15/2024 5:59 AM, Paul E. McKenney wrote:
> On Mon, Oct 14, 2024 at 09:49:52AM -0700, Paul E. McKenney wrote:
>> On Mon, Oct 14, 2024 at 02:45:50PM +0530, Neeraj Upadhyay wrote:
>>> 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/
>>
>> Good eyes!
>
> And fixed.
> >>> This commit is doing a lot more than renaming "cpuc".
>>
>> Indeed, it does look like I forgot to commit between two changes.
>>
>> It looks like this commit log goes with the changes to the
>> functions srcu_readers_lock_idx(), srcu_readers_unlock_idx(), and
>> srcu_readers_active(). With the exception of the change from "NMI-safe"
>> to "reader flavors in the WARN_ONCE() string in srcu_readers_unlock_idx().
>>
>> How would you suggest that I split up the non-s/cpuc/sdp/ changes?
>
> As a first step, I split it three ways, as you can see on the updated "dev"
> branch in the -rcu tree.
>
> Thoughts?
>

Split looks good to me!

- Neeraj

> Thanx, Paul
>
>>> - Neeraj
>>>
>>>> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
>>>> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
>>>> Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
>>>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>>>> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
>>>> Cc: <bpf@xxxxxxxxxxxxxxx>
>>>> ---
>>>> 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 */
>>>

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In reply to: Paul E. McKenney: "Re: [PATCH rcu 05/12] srcu: Standardize srcu_data pointers to "sdp" and similar"
Next in thread: Paul E. McKenney: "[PATCH rcu 10/12] rcutorture: Add srcu_read_lock_lite() support to rcutorture.reader_flavor"
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