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From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
To: peterz@infradead.org
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Sebastian A. Siewior" <bigeasy@linutronix.de>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 4/5] seqlock: seqcount_LOCKNAME_t: Introduce PREEMPT_RT support
Date: Tue, 8 Sep 2020 14:48:50 +0200
Message-ID: <20200908124850.GA487635@lx-t490> (raw)
In-Reply-To: <20200908114520.GS1362448@hirez.programming.kicks-ass.net>

On Tue, Sep 08, 2020 at 01:45:20PM +0200, peterz@infradead.org wrote:
> On Fri, Sep 04, 2020 at 05:32:30PM +0200, Ahmed S. Darwish wrote:
> > @@ -406,13 +443,20 @@ static inline int read_seqcount_t_retry(const seqcount_t *s, unsigned start)
> >  	return __read_seqcount_t_retry(s, start);
> >  }
> >
> > +/*
> > + * Enforce non-preemptibility for all seqcount_LOCKNAME_t writers. Don't
> > + * do it for PREEMPT_RT, for the reasons outlined at __SEQ_LOCK().
> > + */
> > +#define __seq_enforce_writer_non_preemptibility(s)			\
> > +	(!IS_ENABLED(CONFIG_PREEMPT_RT) && __seqcount_lock_preemptible(s))
> > +
> >  /**
> >   * raw_write_seqcount_begin() - start a seqcount_t write section w/o lockdep
> >   * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
> >   */
> >  #define raw_write_seqcount_begin(s)					\
> >  do {									\
> > -	if (__seqcount_lock_preemptible(s))				\
> > +	if (__seq_enforce_writer_non_preemptibility(s))			\
> >  		preempt_disable();					\
> >  									\
> >  	raw_write_seqcount_t_begin(__seqcount_ptr(s));			\
> > @@ -433,7 +477,7 @@ static inline void raw_write_seqcount_t_begin(seqcount_t *s)
> >  do {									\
> >  	raw_write_seqcount_t_end(__seqcount_ptr(s));			\
> >  									\
> > -	if (__seqcount_lock_preemptible(s))				\
> > +	if (__seq_enforce_writer_non_preemptibility(s))			\
> >  		preempt_enable();					\
> >  } while (0)
> >
> > @@ -456,7 +500,7 @@ static inline void raw_write_seqcount_t_end(seqcount_t *s)
> >  do {									\
> >  	__seqcount_assert_lock_held(s);					\
> >  									\
> > -	if (__seqcount_lock_preemptible(s))				\
> > +	if (__seq_enforce_writer_non_preemptibility(s))			\
> >  		preempt_disable();					\
> >  									\
> >  	write_seqcount_t_begin_nested(__seqcount_ptr(s), subclass);	\
> > @@ -483,7 +527,7 @@ static inline void write_seqcount_t_begin_nested(seqcount_t *s, int subclass)
> >  do {									\
> >  	__seqcount_assert_lock_held(s);					\
> >  									\
> > -	if (__seqcount_lock_preemptible(s))				\
> > +	if (__seq_enforce_writer_non_preemptibility(s))			\
> >  		preempt_disable();					\
> >  									\
> >  	write_seqcount_t_begin(__seqcount_ptr(s));			\
> > @@ -504,7 +548,7 @@ static inline void write_seqcount_t_begin(seqcount_t *s)
> >  do {									\
> >  	write_seqcount_t_end(__seqcount_ptr(s));			\
> >  									\
> > -	if (__seqcount_lock_preemptible(s))				\
> > +	if (__seq_enforce_writer_non_preemptibility(s))			\
> >  		preempt_enable();					\
> >  } while (0)
>
> I've replaced the above with the below, afaict there were no users of
> __seqcount_lock_preemptible() left.
>
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -228,7 +228,11 @@ __seqprop_##lockname##_sequence(const se
>  static __always_inline bool						\
>  __seqprop_##lockname##_preemptible(const seqcount_##lockname##_t *s)	\
>  {									\
> -	return preemptible;						\
> +	if (!IS_ENABLED(CONFIG_PREEMPT_RT))				\
> +		return preemptible;					\
> +									\
> +	/* PREEMPT_RT relies on the above LOCK+UNLOCK */		\
> +	return false;							\
>  }									\
>  									\

Sounds good.

  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-04 15:32 [PATCH v2 0/5] seqlock: " Ahmed S. Darwish
2020-09-04 15:32 ` [PATCH v2 1/5] seqlock: seqcount_LOCKNAME_t: Standardize naming convention Ahmed S. Darwish
2020-09-10 15:08   ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish
2020-09-04 15:32 ` [PATCH v2 2/5] seqlock: Use unique prefix for seqcount_t property accessors Ahmed S. Darwish
2020-09-08 11:41   ` peterz
2020-09-10 15:08   ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish
2020-09-04 15:32 ` [PATCH v2 3/5] seqlock: seqcount_t: Implement all read APIs as statement expressions Ahmed S. Darwish
2020-09-10 15:08   ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish
2020-09-04 15:32 ` [PATCH v2 4/5] seqlock: seqcount_LOCKNAME_t: Introduce PREEMPT_RT support Ahmed S. Darwish
2020-09-08 11:45   ` peterz
2020-09-08 12:48     ` Ahmed S. Darwish [this message]
2020-09-04 15:32 ` [PATCH v2 5/5] seqlock: PREEMPT_RT: Do not starve seqlock_t writers Ahmed S. Darwish
2020-09-10 15:08   ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish
2020-09-15  0:20 ` [PATCH v2 0/5] seqlock: Introduce PREEMPT_RT support Qian Cai
2020-09-15 12:48   ` Boqun Feng
2020-09-15 13:10     ` Boqun Feng
2020-09-15 14:30     ` peterz
2020-09-16 12:52       ` Qian Cai
2020-09-16 12:54         ` peterz
2020-09-16 13:00           ` Qian Cai
2020-09-16 13:02             ` peterz
2020-09-17  2:31               ` Stephen Rothwell
2020-09-18  8:42       ` [tip: locking/core] seqlock: Unbreak lockdep tip-bot2 for peterz@infradead.org

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