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Message-ID: <25cd96f1-6d4d-4dba-b57b-da63d228ba97@paulmck-laptop>
Date: Mon, 14 Oct 2024 09:49:52 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Cc: frederic@...nel.org, rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...a.com, rostedt@...dmis.org,
Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Kent Overstreet <kent.overstreet@...ux.dev>, bpf@...r.kernel.org
Subject: Re: [PATCH rcu 05/12] srcu: Standardize srcu_data pointers to "sdp"
and similar
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!
> 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?
Thanx, Paul
> - Neeraj
>
> > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > Cc: Andrii Nakryiko <andrii@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Kent Overstreet <kent.overstreet@...ux.dev>
> > Cc: <bpf@...r.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 */
>
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