Subject: Re: [PATCH v2 3/9] rcu/sync: Remove custom check for reader-section

From: "Paul E. McKenney" <[email-masked]>
Date: Tue, 16 Jul 2019 11:28:16 -0700

On Tue, Jul 16, 2019 at 11:26:42AM -0700, Paul E. McKenney wrote:
> On Fri, Jul 12, 2019 at 01:00:18PM -0400, Joel Fernandes (Google) wrote:
> > The rcu/sync code was doing its own check whether we are in a reader
> > section. With RCU consolidating flavors and the generic helper added in
> > this series, this is no longer need. We can just use the generic helper
> > and it results in a nice cleanup.
> > 
> > Cc: Oleg Nesterov <[email-masked]>
> > Signed-off-by: Joel Fernandes (Google) <[email-masked]>
> 
> This needs to be forward-ported to current mainline.  (Or, I believe
> equivalently for this file, to branch "dev" of -rcu.)
> 
> Especially given that you have Oleg's Ack, I would be happy to
> take the forward-ported version.

Never mind, I am one version behind.  Apologies for the noise!

							Thanx, Paul

> > ---
> > Please note: Only build and boot tested this particular patch so far.
> > 
> >  include/linux/rcu_sync.h |  5 ++---
> >  kernel/rcu/sync.c        | 22 ----------------------
> >  2 files changed, 2 insertions(+), 25 deletions(-)
> > 
> > diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
> > index 6fc53a1345b3..c954f1efc919 100644
> > --- a/include/linux/rcu_sync.h
> > +++ b/include/linux/rcu_sync.h
> > @@ -39,9 +39,8 @@ extern void rcu_sync_lockdep_assert(struct rcu_sync *);
> >   */
> >  static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
> >  {
> > -#ifdef CONFIG_PROVE_RCU
> > -	rcu_sync_lockdep_assert(rsp);
> > -#endif
> > +	RCU_LOCKDEP_WARN(!rcu_read_lock_any_held(),
> > +			 "suspicious rcu_sync_is_idle() usage");
> >  	return !rsp->gp_state; /* GP_IDLE */
> >  }
> >  
> > diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
> > index a8304d90573f..535e02601f56 100644
> > --- a/kernel/rcu/sync.c
> > +++ b/kernel/rcu/sync.c
> > @@ -10,37 +10,25 @@
> >  #include <linux/rcu_sync.h>
> >  #include <linux/sched.h>
> >  
> > -#ifdef CONFIG_PROVE_RCU
> > -#define __INIT_HELD(func)	.held = func,
> > -#else
> > -#define __INIT_HELD(func)
> > -#endif
> > -
> >  static const struct {
> >  	void (*sync)(void);
> >  	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
> >  	void (*wait)(void);
> > -#ifdef CONFIG_PROVE_RCU
> > -	int  (*held)(void);
> > -#endif
> >  } gp_ops[] = {
> >  	[RCU_SYNC] = {
> >  		.sync = synchronize_rcu,
> >  		.call = call_rcu,
> >  		.wait = rcu_barrier,
> > -		__INIT_HELD(rcu_read_lock_held)
> >  	},
> >  	[RCU_SCHED_SYNC] = {
> >  		.sync = synchronize_rcu,
> >  		.call = call_rcu,
> >  		.wait = rcu_barrier,
> > -		__INIT_HELD(rcu_read_lock_sched_held)
> >  	},
> >  	[RCU_BH_SYNC] = {
> >  		.sync = synchronize_rcu,
> >  		.call = call_rcu,
> >  		.wait = rcu_barrier,
> > -		__INIT_HELD(rcu_read_lock_bh_held)
> >  	},
> >  };
> >  
> > @@ -49,16 +37,6 @@ enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
> >  
> >  #define	rss_lock	gp_wait.lock
> >  
> > -#ifdef CONFIG_PROVE_RCU
> > -void rcu_sync_lockdep_assert(struct rcu_sync *rsp)
> > -{
> > -	RCU_LOCKDEP_WARN(!gp_ops[rsp->gp_type].held(),
> > -			 "suspicious rcu_sync_is_idle() usage");
> > -}
> > -
> > -EXPORT_SYMBOL_GPL(rcu_sync_lockdep_assert);
> > -#endif
> > -
> >  /**
> >   * rcu_sync_init() - Initialize an rcu_sync structure
> >   * @rsp: Pointer to rcu_sync structure to be initialized
> > -- 
> > 2.22.0.510.g264f2c817a-goog
> >